diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index af59dbc4..fe73e468 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -72,6 +72,9 @@ SIM_E2E=1 node --test 'test/sim/*.browser.test.js'               # 浏览器里
   `test/docs-consistency.test.js` 固定了文档里的一些句子，改文档后跑一下。
 - 代码和注释用英文；玩家文档（README、PLAYING、DEPLOY）用简体中文，技术文档用英文。界面上的文字写中文并用 `t('…')`
   包起来，英文放进 `public/i18n/en.json`（[docs/I18N.md](docs/I18N.md)）。
+- 翻译成新的语言：一个语言就是 `public/i18n/` 里的一个文件，不用改代码。`node tools/i18n.mjs template <语言代码>` 生成骨架，
+  翻译后用 `node tools/i18n.mjs check <语言代码>` 检查，步骤见 [docs/I18N.md](docs/I18N.md)「Adding a language」；语言包是
+  内容包的第一种，格式见 [docs/PACKS.md](docs/PACKS.md)。
 - 提交的代码以 GPL-3.0-or-later 发布。本项目坚持非商业，请不要加入广告、付费、打赏等任何变现功能。
 
 ## 5. 添加干员（自选编队）
@@ -111,7 +114,9 @@ SIM_E2E=1 node --test 'test/sim/*.browser.test.js'               # 浏览器里
   `Generated with …` (the maintainers' convention) — merged pull requests are credited in the CHANGELOG. Describe the
   sources, the `[ASSUMED]` items, the tests and the golden scenarios that moved; update the docs a rule change makes
   wrong. Code and comments in English; player-facing text in Chinese through `t('…')` with the English in
-  `public/i18n/en.json`. Code is GPL-3.0-or-later; no monetisation features.
+  `public/i18n/en.json`. A new language is one file in `public/i18n/` and no code: `node tools/i18n.mjs template <code>`,
+  translate, `node tools/i18n.mjs check <code>` (docs/I18N.md "Adding a language"; packs in general: docs/PACKS.md).
+  Code is GPL-3.0-or-later; no monetisation features.
 - **Adding an operator (自选)**: follow "How to add an operator (自选)" in
   [server/sim/content/kits/README.md](server/sim/content/kits/README.md): `op-<codename>.js` keyed by the charId,
   registered in `OPERATOR_KIT_FILES`, a test `test/content/op_<codename>.test.js`, the fidelity checklist in the pull
diff --git a/README.md b/README.md
index 5a6e2df4..b30a23b6 100644
--- a/README.md
+++ b/README.md
@@ -185,7 +185,7 @@ npm start          # 启动服务器：http://localhost:3000
 | [docs/META.md](docs/META.md) | 对局与经济引擎（英文）：回合流程、商店、联防、最终攻势的实现细节 |
 | [docs/DATA.md](docs/DATA.md) | 由官方数据表生成的游戏数据（英文） |
 | [docs/ASSETS.md](docs/ASSETS.md) | 素材来源、目录结构与清单（英文） |
-| [docs/I18N.md](docs/I18N.md) | 中文 / English 界面（英文）：界面文字、游戏文本与服务器消息怎样翻译，覆盖范围，切到英文后仍显示中文的内容 |
+| [docs/I18N.md](docs/I18N.md) | 界面语言（英文）：界面文字、游戏文本与服务器消息怎样翻译，覆盖范围；**添加一种语言只需在 `public/i18n/` 放一个语言文件**（社区翻译步骤见「Adding a language」，内容包格式见 [docs/PACKS.md](docs/PACKS.md)） |
 | [docs/BALANCE.md](docs/BALANCE.md) | 难度模型与测量（英文） |
 | [docs/research/](docs/research/00-INDEX.md) | 官方规则、数据与界面的调研记录 |
 
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index 425dda40..bb8cd47f 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -77,6 +77,7 @@ so old imports keep working: `public/js/ui/gameLogic.js` (`public/js/ui/gameLogi
 | `server/net.js` | sessions and reconnect tokens, rate limits, message validation |
 | `server/lobby.js` | rooms, seats, AI seats, spectators; starts a `Match` |
 | `server/data.js` | loads `data/*.json` once (frozen) |
+| `server/packs.js` | the content packs (PACKS.md): finds the language packs of `public/i18n/` and the pack folders of `packs/`, validates them, answers `/packs/index.json` and which pack files may be served; re-reads the folders when they change |
 | `server/match/Match.js` | one match: the phase machine, timers, the round loop, co-op, the views; its methods are in `server/match/match/` (`phases.js`, `prep.js`, `combat.js`, `clientCombat.js`, `reports.js`, `unitePhase.js`, `bossRounds.js`, `settle.js`, `views.js`, `intents.js` …) |
 | `server/match/PlayerState.js` | one player's shop, hand, board, items, bonds and LP, and every prep intent; its methods are in `server/match/player/` (`economy.js`, `acquire.js`, `placement.js`, `items.js`, `pieces.js`, `prep.js`, `round.js`, `diy.js`, `views.js` …) |
 | `server/match/` (the rest) | `pool.js` (the shared chess pool), `board.js` (placement), `bondsMeta.js`, `effectsMeta.js` and `builtinMeta.js` (prep-phase effects), `choices.js` (机变), `waves.js`, `unite.js` (联防), `finalAssault.js`, `results.js`, `bot.js` (AI players and AI 托管), `fields.js` (the battles of a combat phase), `scheduler.js`, `gamedata.js` |
@@ -88,7 +89,7 @@ so old imports keep working: `public/js/ui/gameLogic.js` (`public/js/ui/gameLogi
 | `server/sim/content/garrisons/`, `items/`, `bands/` | 特质, equipment and strategies: `battle.js` is the battle side, `meta.js` the prep side (`registerMeta`, META §2) |
 | `server/sim/content/bonds/` | the 23 bonds: `core.js` the 8 core bonds (both sides), `server/sim/content/bonds/addon/` the 15 add-on bonds (`battle.js`, `meta.js`) |
 | `server/sim/content/` (the rest) | `tokens.js` (summons), `devices.js` (terrain and stage devices), `generic.js` (the kit built from a skill's data when a chess has none), `choices.js` (机变 cards in battle) |
-| `shared/` | imported by the server and the browser: `protocol.js`, `constants.js`, `i18n.js` and `i18nData.js`, `standIn.js` (补位), `diy.js` (自选编队), `highGround.js`, `loadoutRecord.js` |
+| `shared/` | imported by the server and the browser: `protocol.js`, `constants.js`, `i18n.js`, `i18nData.js` and `i18nPacks.js` (languages), `packs.js` (the content-pack format), `standIn.js` (补位), `diy.js` (自选编队), `highGround.js`, `loadoutRecord.js` |
 
 ### Client (`public/`)
 
@@ -100,14 +101,15 @@ so old imports keep working: `public/js/ui/gameLogic.js` (`public/js/ui/gameLogi
 | `public/js/screens/` | `title.js`, `lobby.js`, `room.js`, `loadout.js` (干员调配), `ownership.js` (干员持有), `diy.js` (自选编队), `briefing.js`, `bandDraft.js`, `game.js` with `public/js/screens/game/`, `result.js` |
 | `public/js/ui/` | the HUD components (`hud.js`, `shopBar.js`, `detailPanel.js`, `bondStrip.js`, `teamPanel.js` …); `public/js/ui/gameLogic/` the pure in-match logic, unit-tested in Node |
 | `public/js/render/` | the field view: `app.js` with `public/js/render/app/`, `units.js` and `spine.js` (models), `tiles.js`, `projection.js`, `interp.js`, `pick.js`, `drag.js`, `public/js/render/fx/` (effects; `kinds.js` maps the fx kinds), `public/js/render/board3d/` (the official 3D board) |
-| `public/css/`, `public/i18n/en.json` | the styles; the English UI strings |
+| `public/css/`, `public/i18n/<code>.json` | the styles; the UI strings of each language pack (English ships) |
 
 ### Data, tools, tests
 
 | path | what |
 |---|---|
-| `data/*.json` | generated by `tools/build-data.mjs` and committed — never edited by hand (DATA.md); `data/backups.json` holds the 补位 and 自选 data, `data/i18n/en.json` the English game texts, `data/assets.json` the art manifest |
-| `tools/` | `build-data.mjs`, `build-i18n.mjs`, `i18n.mjs` (UI strings), `setup.mjs` / `fetch-assets.mjs` / `tools/assets/` (art and audio), `tools/local-extract/` (art from a local game client), `vendor.mjs`, `golden.mjs`, `check-imports.mjs`, `package.mjs` (the release zip), `doctor.mjs`; sweeps: `matchrun.mjs`, `simrun.mjs`, `botbench.mjs`, `balance.mjs` |
+| `data/*.json` | generated by `tools/build-data.mjs` and committed — never edited by hand (DATA.md); `data/backups.json` holds the 补位 and 自选 data, `data/i18n/<code>.json` the game texts of a language pack (English), `data/assets.json` the art manifest |
+| `packs/` | content packs installed as folders, `packs/<id>/pack.json` + files (PACKS.md); empty in the repository but for its readme |
+| `tools/` | `build-data.mjs`, `build-i18n.mjs`, `i18n.mjs` (UI strings, language packs), `packs.mjs` (content packs), `setup.mjs` / `fetch-assets.mjs` / `tools/assets/` (art and audio), `tools/local-extract/` (art from a local game client), `vendor.mjs`, `golden.mjs`, `check-imports.mjs`, `package.mjs` (the release zip), `doctor.mjs`; sweeps: `matchrun.mjs`, `simrun.mjs`, `botbench.mjs`, `balance.mjs` |
 | `test/` | `node:test` suites by area: `test/content/` (kits, enemies, bonds, items), `test/sim/` (the engine), `test/match/` (match engine, bots), `test/ui/`, `test/render/`, `test/golden/` (the stored digests), `test/helpers/` (`battleHarness.js`; `designDocs.js`, the design document in § order for the doc tests), `test/e2e/` (browser and bot runs) |
 | `types/` | JSDoc typedefs of the type-checked slice (`types/README.md`) |
 | `docs/` | the documents; `docs/DESIGN.md` the index of the design document, `docs/design/` its current rules, `docs/history/` its per-release revisions; `docs/research/` the research on the official mode |
@@ -135,10 +137,11 @@ public/assets/ ─────────▶ public/js/render/, public/js/audio
   the sim through `server/sim/simdata.js`, which turns every record into a frozen engine def.
 - **In the browser**, `public/js/data.js` fetches the same files once per page for the UI, and the battle runner loads
   its own frozen copies for the sim (`loadBrowserSim` → `setSimData`), so both sides simulate from the same data.
-- **Languages.** Chinese is the source language. The English game texts come from the official EN client
-  (`tools/build-i18n.mjs` → `data/i18n/en.json`, applied by `public/js/data.js`); UI strings are wrapped in `t('…')`
-  and translated in `public/i18n/en.json` (`tools/i18n.mjs` lists what is missing); server messages travel as message
-  ids. I18N.md.
+- **Languages.** Chinese is the source language; every other language is a pack — `public/i18n/<code>.json` (UI
+  strings) and optionally `data/i18n/<code>.json` (game texts), listed by the server at `/packs/index.json`
+  (`server/packs.js`; PACKS.md). The English game texts come from the official EN client (`tools/build-i18n.mjs` →
+  `data/i18n/en.json`, applied by `public/js/data.js`); UI strings are wrapped in `t('…')` and translated in the packs
+  (`tools/i18n.mjs` lists what is missing); server messages travel as message ids. I18N.md.
 - **Art and audio** are never committed. `npm run setup` downloads them from public mirrors (`tools/fetch-assets.mjs`,
   planned by `tools/assets/plan.mjs`) into `public/assets/` and writes the manifest `data/assets.json`;
   `tools/local-extract/` can add art from a local game client. The client only requests URLs listed in the manifest.
@@ -181,6 +184,7 @@ public/assets/ ─────────▶ public/js/render/, public/js/audio
 | a screen or a HUD panel | `public/js/screens/`, `public/js/ui/`; pure logic in `public/js/ui/gameLogic/` | `test/ui/` |
 | battle visuals | `public/js/render/fx/kinds.js`, `public/js/render/units.js`, `public/js/render/spine.js` | `test/render/` |
 | a UI text | `t('…')` in the code, the English in `public/i18n/en.json` | I18N.md |
+| a language | `public/i18n/<code>.json` (`node tools/i18n.mjs template <code>`), no code | I18N.md "Adding a language", PACKS.md |
 | HTTP, headers, static routes | `server/http/` | `test/version.test.js`, `test/client-static.test.js` |
 
 Before changing a rule, read the DESIGN section that owns it (module headers cite their sections; the table in
diff --git a/docs/DEPLOY.md b/docs/DEPLOY.md
index a4fc61d3..9dec6b02 100644
--- a/docs/DEPLOY.md
+++ b/docs/DEPLOY.md
@@ -300,7 +300,7 @@ npm run package -- --out <目录>        # 完整包 Stronghold-Protocol-v<版
 npm run package:lite -- --out <目录>   # 精简包 Stronghold-Protocol-v<版本>-lite.zip
 ```
 
-- **打进去的**：`git ls-files` 里的 `server/`、`shared/`、`data/`、`public/`（不含 `public/dev/`）、启动脚本、玩家会运行的工具（setup、vendor、fetch-assets 与 `tools/assets/`、doctor，以及 setup 调用的 `tools/local-extract/` 和 `crop-board-atlas.mjs`）、服务器和 fetch-assets 读取的 4 张研究数据表（`docs/research/` 的 `03-operators`、`05-enemies`、`05-maps`、`07-assets` 四个 JSON）、`package.json` / `package-lock.json`、许可证与说明（`LICENSE`、`NOTICE.md`、`THIRD-PARTY-NOTICES.md`、`README.md`、`CHANGELOG.md`）、`docs/PLAYING.md` 和本文；然后在临时目录里 `npm ci --omit=dev` 装上运行依赖和 `public/vendor`。完整包再加上 `data/assets.json` 列出的素材、`public/fonts`，以及本地提取的 `public/assets/local/` 和 `data/local-assets.json`。磁盘上有、清单却没列出的文件不打进去（例如 0.2.0 移出自选的焰狐龙梓兰的旧素材）。
+- **打进去的**：`git ls-files` 里的 `server/`、`shared/`、`data/`、`public/`（不含 `public/dev/`）、`packs/`（随仓库提交的内容包；只在本机安装、没提交的不打进去）、启动脚本、玩家会运行的工具（setup、vendor、fetch-assets 与 `tools/assets/`、doctor，以及 setup 调用的 `tools/local-extract/` 和 `crop-board-atlas.mjs`）、服务器和 fetch-assets 读取的 4 张研究数据表（`docs/research/` 的 `03-operators`、`05-enemies`、`05-maps`、`07-assets` 四个 JSON）、`package.json` / `package-lock.json`、许可证与说明（`LICENSE`、`NOTICE.md`、`THIRD-PARTY-NOTICES.md`、`README.md`、`CHANGELOG.md`）、`docs/PLAYING.md` 和本文；然后在临时目录里生成 `packs/index.json`（打进去的语言包和内容包的列表，供纯静态托管使用；服务器自己会实时列出，见 [PACKS.md](PACKS.md)），再 `npm ci --omit=dev` 装上运行依赖和 `public/vendor`。完整包再加上 `data/assets.json` 列出的素材、`public/fonts`，以及本地提取的 `public/assets/local/` 和 `data/local-assets.json`。磁盘上有、清单却没列出的文件不打进去（例如 0.2.0 移出自选的焰狐龙梓兰的旧素材）。
 - **不打进去的**：`test/`、维护用的工具（数据构建、golden、botbench、i18n、导入检查、本工具等）、`scripts/make-windows-bundle.mjs`（Windows 便携包，见 [WINDOWS.md](WINDOWS.md)）、其他文档、研究笔记和 `docs/img/`、`handoff/`、`.github/`、`types/`、lint / 编辑器 / Docker 配置。和 0.1.x 的整树打包相比，完整包少了约 570 个文件、解压后小约 25 MB，zip 小约 8 MB。
 - **打包前的检查**（`--dry-run` 也全部做一遍）：拒绝名单（`pv`、`review`、`.cache`、`.claude`、`.git`、`logs`、`.env`、`scripts/service.env.cmd`、`handoff`、`test` 等）；每个打进去的模块的相对导入、玩家用的 npm 脚本（start / setup / doctor / launch / postinstall / vendor / assets）都指向包里的文件；完整包里 `data/assets.json` 和 `data/local-assets.json` 列出的文件都在（缺了先运行 `node tools/fetch-assets.mjs`）；没有只差大小写的两个路径；包里的文件（二进制素材也查）不含个人目录路径（`/Users/…`、`C:\Users\…`、`/home/…`）或本机的账户名（运行时从系统读取；`SP_PACKAGE_SCAN_NAMES=a,b` 可以再加名字）；打进去的已跟踪文件没有未提交的改动（重新生成的 `data/assets.json` 要先提交）。有任何问题都会列出原因、以非零状态结束，不写 zip；正式打包时还会核对临时目录里的文件和计划完全一致。
 - **需要**：已下载素材的仓库（完整包）——打包前先联网运行一次 `node tools/fetch-assets.mjs`，补齐清单计划但本机还没有的素材（清单只列出磁盘上有的文件，打包工具看不出缺了哪些；`data/assets.json` 有变化就先提交）；能访问 npm 的网络（`npm ci`）；`zip`（或 bsdtar 的 `tar`，Windows 10 起自带）。`--out` 默认是系统临时目录下的 `stronghold-protocol-release`，不能在仓库里面；`--force` 覆盖已有的 zip，`--keep-stage` 保留打包用的目录供检查。
diff --git a/docs/I18N.md b/docs/I18N.md
index 2da6ecd0..d308c7e0 100644
--- a/docs/I18N.md
+++ b/docs/I18N.md
@@ -1,17 +1,22 @@
-# I18N.md — languages (中文 / English)
+# I18N.md — languages (中文, English, language packs)
 
-Chinese is the default; English is a switch (the owner's decision of 2026-10-05): an English browser still opens in
-Chinese until the player picks English on the title screen (top right) or in 设置 / Settings. The choice is kept in
-`localStorage` (`sp.pref.lang`); `?lang=en` / `?lang=zh` in the address bar sets it once and is then removed. A switch
-re-renders the page in place (no reload).
+Chinese is the default; every other language is a switch (the owner's decision of 2026-10-05): an English browser still
+opens in Chinese until the player picks a language on the title screen (top right) or in 设置 / Settings. Every
+language but Chinese is a **language pack** — a file in the language folder, nothing else (the owner's decision of
+2026-10-07; §5 "Adding a language"): the menu lists every pack the server finds, each under its own name (buttons up to
+four languages, a list beyond). English is a pack like any other; it ships with the game and is the complete one. The
+choice is kept in `localStorage` (`sp.pref.lang`); `?lang=<code>` in the address bar (`?lang=en`, `?lang=zh`) sets it
+once and is then removed; a stored language whose pack is gone opens in Chinese. A switch re-renders the page in place
+(no reload). Language packs are the first type of the content packs (docs/PACKS.md: the manifest, the registry, the
+index, the pack folders).
 
 Three kinds of text, three mechanisms — no i18n framework:
 
-| Text | Source of the English | Mechanism |
+| Text | Source of a language | Mechanism |
 |---|---|---|
-| UI strings (buttons, labels, hints, toasts) | `public/i18n/en.json` — Chinese msgid → English | `t()` in the code (`shared/i18n.js`) |
-| Game texts (operators, skills, talents, modules, traits, enemies, bonds, items, effects, strategies, 特质, 机变 cards, modes, stages, tokens) | `data/i18n/en.json` — the official EN client texts by record id and field | `public/js/data.js` returns localized records |
-| Server messages (m.toast, m.ticker, error codes) | the same `public/i18n/en.json` | the server sends msgid + params, the client translates |
+| UI strings (buttons, labels, hints, toasts) | `public/i18n/<code>.json` — Chinese msgid → translation (English: `public/i18n/en.json`) | `t()` in the code (`shared/i18n.js`) |
+| Game texts (operators, skills, talents, modules, traits, enemies, bonds, items, effects, strategies, 特质, 机变 cards, modes, stages, tokens) | `data/i18n/<code>.json` — the official client texts by record id and field (English: the EN client) | `public/js/data.js` returns localized records |
+| Server messages (m.toast, m.ticker, error codes) | the same `public/i18n/<code>.json` | the server sends msgid + params, the client translates |
 
 ## 1. UI strings: `t()`
 
@@ -27,9 +32,25 @@ const TABLE = { a: N_('独立模拟') };     // module level: N_ only marks it;
 html`<span>${tParts('第 {r} 回合 · 最终攻势', { r: html`<b class="num">${r}</b>` })}</span>`; // markup inside a sentence
 ```
 
-- **Placeholders** are the same in the msgid and the translation: `{name}`, positional `{0}`, and one plural form for
-  English, `{n|one|other}` (`'{n} {n|round|rounds}'`). A value that is an array renders as a list (`、` / `, `). A
-  missing value leaves the placeholder as it is (official templates such as `{0}博士…` pass through untouched).
+- **Placeholders** are the same in the msgid and the translation: `{name}`, positional `{0}`, and plural forms. Two
+  plain forms `{n|one|other}` (`'{n} {n|round|rounds}'`) pick `one` when the language's plural category of the number
+  is `one` (`Intl.PluralRules`; in English when n is 1 — as before packs, but for −1, now singular) and `other` otherwise. A language with
+  more categories names them: `{n|one:секунда|few:секунды|many:секунд|other:секунды}` (categories `zero`, `one`, `two`,
+  `few`, `many`, `other`; `other` is required; three or more plain forms are refused — the order of a language's
+  categories differs between engines). A plural form holds no placeholder of its own: write the number beside it
+  (`{n} {n|…}`). A value that is an array renders as a list joined with the language's separator (its translation of
+  `list::、`; `、` in Chinese, `, ` without one). A missing value leaves the placeholder as it is (official templates such
+  as `{0}博士…` pass through untouched).
+- **Validation.** A translation must keep every plain `{name}` of its msgid (a plural form does not count: it does not
+  show the number), and may use another name only when the caller passes it (`'{n} {count|unit|units}'` with `count`
+  passed beside a markup `n`). A translation that drops or invents a placeholder, or has a broken plural form, is
+  skipped like a missing one — the next language of the chain shows — and reported once on the console of a
+  development page (a dev build, or a page served from this machine: localhost); `node tools/i18n.mjs check` flags it
+  against the call sites.
+- **Fallback chain**, per string: the chosen pack → its base (`_meta.base`, else the language of a regional code:
+  `pt-BR` → `pt` when there is a `pt` pack; `zh-TW` has none — Chinese is the source) with the base's own chain → the
+  packs its `_meta.fallback` names (`["en"]`: what it lacks shows in English) → the Chinese msgid. A partial pack is
+  fine. `tc()` tries its context key and then the plain msgid in each language before the next one.
 - **Markup inside a sentence** (a number in `<b>`, a `<kbd>`): `tParts(msgid, params)` returns the translation split at
   its placeholders, with a param that is markup (a vnode, or an array of vnodes) kept as it is — the translator gets the
   whole sentence and its word order, the Chinese pieces are the text around the markup exactly as before. Do not split
@@ -46,10 +67,13 @@ html`<span>${tParts('第 {r} 回合 · 最终攻势', { r: html`<b class="num">$
 
 ### Translating
 
-Edit `public/i18n/en.json` (`"msgid": "English"`, two-space JSON; `_about` is metadata). Keep every `{placeholder}`;
-`test/i18n.test.js` checks that, that no Chinese is left in a value, and that every msgid the code uses is present. A
-translation may use more params than its msgid (`'{n} {count|unit|units}'` with `count` passed beside a vnode `n`). Use
-the official EN terms of the game (the EN client's own wording, e.g. its tips and mode texts):
+Edit the pack, e.g. `public/i18n/en.json` (`"msgid": "English"`, two-space JSON; `_meta` is its manifest, `_about` a
+note; keys starting with `_` are never strings). Keep every `{placeholder}` (above); `test/i18n.test.js` checks that,
+that no Chinese is left in an English value, and that every msgid the code uses is in English — English declares
+`"complete": true`, and `node tools/i18n.mjs check --strict` holds a complete pack to every msgid, a partial pack only to
+its placeholders. A translation may use more params than its msgid (`'{n} {count|unit|units}'` with `count` passed
+beside a vnode `n`). Use the official terms of the game (for English the EN client's own wording, e.g. its tips and mode
+texts):
 
 | 中文 | English | 中文 | English |
 |---|---|---|---|
@@ -69,8 +93,16 @@ the official EN terms of the game (the EN client's own wording, e.g. its tips an
 - `extract [paths] [--list]` — per file: the msgids in `t()` / `tc()` / `tParts()` / `N_()` / `msg()`, and the Chinese
   literals still shown untranslated; the total says how many of those already have a translation (ready for the
   codemod).
-- `check [paths] [--strict] [--stale]` — msgids the code uses that `public/i18n/en.json` lacks (`--strict` exits 1;
-  `--stale` lists entries no code uses yet).
+- `check [<code>… | --all] [paths] [--strict] [--stale] [--list]` — per language pack (default `en`): how many of the
+  msgids the code uses it translates, and its errors — a translation that drops a placeholder, uses one no call site
+  passes, or has a broken plural form; a value that is not a string; a manifest problem. Missing strings are listed for
+  a complete pack (English) or with `--list`; `--stale` lists entries no code uses and no complete pack has. `--strict`
+  exits 1 on an error, or when a complete pack misses a msgid. `--root <dir>` reads the packs of another checkout.
+- `template <code> [--fill <code>]` — writes `public/i18n/<code>.json`: a `_meta` manifest to fill in (the names from
+  `Intl.DisplayNames`, `"fallback": ["en"]` — none for a Chinese variant, whose gaps show the Chinese msgid) and every
+  msgid with an empty value in the order of English (`--fill en`: English values to overwrite). On an existing pack it
+  keeps the translations and `_meta` and adds the msgids the pack lacks — run it again after an update.
+- `index` — the same as `node tools/packs.mjs index` (the pack index for a static host, docs/PACKS.md).
 - `codemod <files> [--write]` — wraps a file's Chinese literals: html`` text and attribute values → `${t('…')}`, strings →
   `t('…')`, template literals → `t('…{name}…', { name })` (an expression's param name: identifier → itself, `a.b` → `b`,
   `x.length` → `n`, else its position), nested strings in params included; adds the import. Module-level literals get
@@ -92,18 +124,22 @@ line marked `// i18n-ignore` and a file marked `i18n-ignore-file` in a comment (
 `test/i18n.test.js` scans what `extract` / `check` scan (public/js, shared, server) and fails on a Chinese literal left
 unwrapped or a msgid missing from `public/i18n/en.json` — `extract` 0 and `check --strict` are part of the tests.
 
-## 2. Game texts: `data/i18n/en.json`
+## 2. Game texts: `data/i18n/<code>.json`
 
 ```
 node tools/build-i18n.mjs                 # downloads the EN tables once into .cache/gamedata-en/, writes data/i18n/en.json
 node tools/build-i18n.mjs --offline       # never download (the zh_CN tables come from .cache/gamedata, as for build-data)
 node tools/build-i18n.mjs --check         # exit 1 when data/i18n/en.json is out of date (nothing written)
 node tools/build-i18n.mjs --source yostar # the other EN source (see below)
+node tools/build-i18n.mjs --lang ja       # another official client: ja (JP), ko (KR), zh-TW (TW) → data/i18n/<code>.json
+node tools/build-i18n.mjs --lang fr --dict fr-texts.json   # no official client: a community dictionary (below)
 ```
 
 **Rebuild it after every `node tools/build-data.mjs`** that changes a text: `test/i18n-data.test.js` fails while a
 translation's Chinese source no longer matches `data/*.json`, and at run time such a stale leaf is not applied (the
-player sees the current Chinese text, never an outdated number).
+player sees the current Chinese text, never an outdated number). The same holds for the game texts of every pack: a
+stale text of a pack falls back like a missing one (the next overlay of its chain, then Chinese) until the pack is
+rebuilt.
 
 - **Sources.** The English comes from the official EN client tables. Default `--source assets`:
   [ArknightsAssets/ArknightsGamedata](https://github.com/ArknightsAssets/ArknightsGamedata) `en/gamedata` — current, and
@@ -131,9 +167,27 @@ player sees the current Chinese text, never an outdated number).
   data. What stays Chinese is CN-only content the EN client does not have yet: some of the 71 owned 6★ of the 自选
   pool (names, skills, talents) and some newer modules (before the 自选 data: 14 931 texts, 99.9 %). Per kind in `.cache/build-i18n-report.json` (also `missing`:
   every untranslated text) and in `meta.coverage`.
-- **Client**: `data.setLocale(lang)` downloads the overlay once (~1.5 MB, ~190 KB gzipped) and from then on `get`,
-  `lookup` and `list` (and every getter built on them) return localized copies; `data.getRaw(name)` keeps the Chinese
-  file; `data.localeName(zh)` translates a name.
+- **Other official clients** (`--lang`): ArknightsAssets/ArknightsGamedata also mirrors the JP, KR and TW clients
+  (`jp/`, `kr/`, `tw/gamedata`), each with both 盟约 seasons (checked 2026-10-07): `--lang ja`, `ko` and `zh-TW` build the
+  game texts of a pack of that language the same way (measured on that day: ja 96.5 %, ko 97.4 %, zh-TW 91.1 % of the
+  22 114 texts — the TW data is older, 51.2, and a Traditional text equal to the Simplified one counts as untranslated
+  although it shows the same). The remake's own strings (stage-name composites, the fallback files) are English only;
+  for another language the pack's UI file (`public/i18n/<code>.json`) is the fallback dictionary, and what is left falls
+  back per text at run time (the pack's chain, then Chinese). Only English is generated in the repository: a game-text
+  overlay ships with the UI pack of its language (a pack is listed by its UI file).
+- **A language without an official client** (French, German, Russian …) needs no game texts at all: they follow the
+  pack's chain (`"fallback": ["en"]` shows the English ones). To translate some, write a community dictionary — a flat
+  JSON `{ "<Chinese data text>": "<translation>" }`; the `names` of `data/i18n/en.json` (every game-data name with its
+  English) is a good first list — and run `node tools/build-i18n.mjs --lang <code> --dict <file.json>`: it writes
+  `data/i18n/<code>.json` from the dictionary and the pack's UI file (exact matches only: a text whose numbers build-data
+  resolved needs its own entry), and every text it does not cover falls back per text at run time. `--dict` also adds to
+  an official client (tried after it).
+- **Client**: `data.setLocale(lang, chain)` downloads the overlays of the chain once each — the pack's own, its base's,
+  a fallback's (`ui/lang.js dataChain`: the languages of the pack's chain that have game texts, with the URLs the pack
+  index gives; English ~1.5 MB, ~190 KB gzipped) — and from then on `get`, `lookup` and `list` (and every getter built
+  on them) return localized copies, **each text from the first overlay of the chain that has it**, else the Chinese one
+  (`shared/i18nData.js applyFileOverlay(json, overlay, onto)`); `data.getRaw(name)` keeps the Chinese file;
+  `data.localeName(zh)` translates a name through the chain.
 
 ## 3. Server messages
 
@@ -181,6 +235,36 @@ Not player text, never translated: developer details and logs (`detail`, `log.*`
 (`shared/highGround.js` reads the trait text 「可以放置于远程位」), the development STUB match, and the HTTP error pages,
 which are bilingual on purpose.
 
+## 5. Adding a language
+
+A language is a file in the language folder; the server lists it on the next page load (no restart, no build step, no
+code change). For a community translator:
+
+1. **Get the code and the tools**: a clone of the repository and `npm install` (the checker reads the code's msgids).
+   Pick the language's BCP 47 code in its usual case: `ja`, `ko`, `fr`, `pt-BR`, `zh-TW`.
+2. **Make the skeleton**: `node tools/i18n.mjs template <code>` writes `public/i18n/<code>.json` — the `_meta` manifest
+   and every msgid (about 1 000) with an empty value, in the order of the English pack (`--fill en` fills in the English
+   to overwrite). Fill in `_meta`: `name` (the language in itself, shown in the menu), `englishName`, `authors`,
+   `version`; keep `"fallback": ["en"]` to show English where a string is still empty (drop it to show Chinese); set
+   `numberUnits` if the language counts large numbers in 10⁴ steps like Chinese (`["万", "億"]`).
+3. **Translate** the values (empty = not yet: it falls back). Keep every `{placeholder}` of the msgid; plural forms as
+   in §1; `public/i18n/en.json` is the reference for meaning and context (`ctx::msgid` keys are the same Chinese text in
+   another context). Use the official terms of your language's client where it has one.
+4. **Check and try**: `node tools/i18n.mjs check <code>` — coverage, and errors to fix (a dropped or unknown
+   placeholder, a broken plural form). Start the server (`npm start`), pick the language on the title screen; a
+   translation the game skips is reported on the browser console. `node tools/packs.mjs list` says why a pack is not
+   listed (a file name not in its usual case, broken JSON …).
+5. **Game texts** (optional): with an official client of the language, `node tools/build-i18n.mjs --lang <code>` writes
+   `data/i18n/<code>.json` (§2); without one, the game texts follow the chain, or a dictionary translates some of them
+   (`--dict`, §2). Share the pack as a pull request (the
+   file, plus the game-text file if built), or as a folder pack that a server installs by copying it into `packs/`
+   (`packs/<id>/pack.json` naming `ui.json` and `data.json`: docs/PACKS.md). After a game update, run `template <code>`
+   again: it keeps the translations and adds the new msgids.
+
+The tests: `test/i18n-packs.test.js` (discovery, the fallback chain, placeholders, plurals in English and Russian, the
+template and check commands, and that the Chinese and English output of `t()` is what it was before packs: every msgid
+of `public/i18n/en.json` rendered with sample params, compared with the renderer of 0.2.0 before packs).
+
 ## Credits
 
 The English UI strings were seeded from GitHub PR #70 (branch `en-translation`) by **@YuriRestia**, reused with credit
diff --git a/docs/PACKS.md b/docs/PACKS.md
new file mode 100644
index 00000000..f6d29462
--- /dev/null
+++ b/docs/PACKS.md
@@ -0,0 +1,164 @@
+# PACKS.md — content packs
+
+A **content pack** is add-on content a server picks up from a folder: a manifest plus its files. The owner's decision of
+2026-10-07 made the language pack the first type of one general mechanism, so that later resource packs (art, audio,
+fonts) and server-side data packs reuse the same manifest, registry and index instead of each inventing its own. In
+0.2.0 one type loads, **`lang`** (a language: docs/I18N.md "Adding a language"); `assets` and `data` are planned.
+
+| File | Role |
+|---|---|
+| `shared/packs.js` | the format: the manifest, the pack types (`PACK_TYPES`), app version ranges, the index (browser, server and tools) |
+| `shared/i18nPacks.js` | the `lang` type: language codes, the language fields, the fallback chain, the script family |
+| `server/packs.js` | the registry: discovery, validation, the index, which pack files may be served |
+| `server/http/static.js` | `GET /packs/index.json` (the live index) and `GET /packs/<id>/<file>` |
+| `public/js/ui/lang.js` | the client of the `lang` entries: the language menu and the loader |
+| `tools/packs.mjs` | `list`, `index` (the index file for a static host), `check` |
+| `tools/package.mjs` | ships the committed packs and writes `packs/index.json` into the release zips |
+
+## 1. Layouts
+
+Two layouts, read by the same registry and listed alike:
+
+```
+packs/<id>/pack.json + its files      a folder pack — any type; the manifest names its files
+public/i18n/<code>.json               a single-file language pack — its manifest is the file's `_meta` block
+data/i18n/<code>.json                   (+ its game texts, when present)
+```
+
+The single file is the quickest way for a translator (one file, the format English has always had, and how English
+ships); the folder is the layout every pack type shares — a pack distributed as one folder with its own readme and
+licence, and the only layout a resource or data pack will have. A language can come either way; the menu does not tell
+them apart.
+
+The id of a folder pack is its folder name; the id of a single-file language pack is its language code. Ids are
+letters, digits, `.`, `_` and `-` (at most 64), unique across types and without regard to case (Windows and macOS
+would see one folder).
+
+## 2. The manifest
+
+`packs/<id>/pack.json`, or the `_meta` block of `public/i18n/<code>.json` (the same fields):
+
+```json
+{
+  "type": "lang",
+  "lang": "ja",
+  "name": "日本語",
+  "englishName": "Japanese",
+  "version": "1.0.0",
+  "app": ">=0.2.0",
+  "authors": ["…"],
+  "credits": "…",
+  "license": "CC-BY-4.0",
+  "fallback": ["en"],
+  "files": { "ui": "ui.json", "data": "data.json" }
+}
+```
+
+| Field | Meaning |
+|---|---|
+| `id` | optional: the folder or file name decides; a manifest that names another id gets a warning |
+| `type` | `lang` (a single-file language pack may leave it out); planned: `assets`, `data` |
+| `version` | the pack's own version |
+| `app` | the app versions it is made for, a range: `>=0.2.0`, `>=0.2.0 <0.3.0`, `0.2.x`, `^0.2.0`, `~0.2.1`, `*`, alternatives with `||`. A pre-release (0.2.0-dev) counts as its release. Outside the range a language pack still loads — what it lacks falls back — and is flagged `compatible: false` (the server log, `tools/packs.mjs list`); a later type decides what an incompatible pack means for it |
+| `name`, `englishName` | the name in its own language (a language pack: the language's own name, shown in the menu) and in English (the menu's tooltip) |
+| `authors`, `credits`, `license` | who made it; free text (`license`: an SPDX id or text) |
+| `files` | a folder pack: role → path inside the folder. Each type lists its roles and their extensions (`lang`: `ui` required, `data` optional, both `.json`) |
+| the type's fields | `lang`: `lang`, `base`, `fallback`, `complete`, `numberUnits` (docs/I18N.md) |
+
+A **problem** keeps a pack from loading (unknown type, no `lang`, a file missing or outside the folder, broken JSON, an
+id or a language already taken — the language folders' files come first, then the folders by id); a **warning** does
+not (an id that differs, an app range this version is outside of, an unknown file role). Both are printed when the
+server starts or notices a change, and by `node tools/packs.mjs list`.
+
+## 3. Discovery and the index
+
+The server's registry (`server/packs.js`) scans `public/i18n/`, `data/i18n/` and `packs/` when it starts and again
+whenever something there changes: on a request for the index or a pack file it compares the names, sizes and times of
+the files it reads (at most once a second, a few `stat` calls) and scans again if they differ. A pack dropped into a
+folder shows on the next page load — no restart, no build step; a removed one leaves (a player whose stored language is
+gone gets Chinese).
+
+`GET /packs/index.json` (never cached) answers the packs of supported types:
+
+```json
+{ "version": 1, "app": "0.2.0", "packs": [
+  { "id": "en", "type": "lang", "name": "English", "englishName": "English", "version": "0.2.0", "app": ">=0.2.0",
+    "compatible": true, "authors": ["…"], "lang": "en", "fallback": [], "complete": true, "strings": 1017,
+    "files": { "ui": "/i18n/en.json", "data": "/data/i18n/en.json" } } ] }
+```
+
+`files` holds URLs on this server, so a client never builds a path itself. A client reads the entries of its type
+(`readPackIndex(json, 'lang')`: an entry of another type, with a bad id or a URL that is not a path on this server is
+dropped).
+
+**A static host** cannot list folders: `node tools/packs.mjs index` writes the same body to `packs/index.json`
+(git-ignored), and `tools/package.mjs` writes it into the release zips. The live server answers `/packs/index.json`
+itself and ignores that file. Serving the game from plain files needs the server's URL layout: `public/` at `/`,
+`data/` at `/data/`, `shared/` at `/shared/`, `server/sim/` at `/sim/` and `packs/` at `/packs/` (the game itself still
+needs the Node server for its rooms; DEPLOY.md).
+
+**What is served.** `GET /packs/<id>/<file>` answers only a file that the manifest of a loaded folder pack names under a
+role of its type, with that role's extension, inside the folder once links are resolved — `pack.json`, a readme, an
+HTML or script file in the folder are never served; a pack of a planned type serves nothing. A single-file language
+pack's files are the language folders' own (`/i18n/<code>.json`, `/data/i18n/<code>.json`).
+
+## 4. The types
+
+| Type | Status | Where it applies | Loader |
+|---|---|---|---|
+| `lang` | supported (0.2.0) | the client: UI strings, game texts | `public/js/ui/lang.js` (the menu, the strings: `shared/i18n.js`; the game texts: `public/js/data.js`) |
+| `assets` | planned | the client: art, audio, font replacements | — |
+| `data` | planned | the server: data patches applied at start | — |
+
+A pack of a planned type is parsed and listed as not supported ("type "assets" is planned …, not loaded by this
+version"); it is never served and never changes anything.
+
+### Adding a pack type
+
+1. **The type** — its entry in `PACK_TYPES` (`shared/packs.js`): `status`, `summary`, `live` (whether a running server
+   may take changes without a restart) and `files` (the roles a folder pack names, with the extensions that may be
+   served for each). Its own manifest fields get a normalizer beside `langFields` and a branch in `normalizeManifest`;
+   its index fields a branch in `packIndexEntry`.
+2. **The loader** — reads the registry by type: `createPackRegistry(…).list('assets')` on the server, or the index
+   entries of the type in the browser (`readPackIndex(json, 'assets')`), the way `ui/lang.js` reads `lang`. A
+   server-side type (`data`) loads once at start (`live: false`): the simulation's code and data are fixed for the life
+   of the process, and a battle must run the same data on the server and in every browser.
+3. **The checks** — what `tools/packs.mjs check` and the tests verify for the type (a data pack: the same validation
+   the data builder applies; a resource pack: the files exist and are of the allowed kinds), and its documentation
+   here.
+
+Things later types must keep (the maintainers' study of mods, 2026-10-07):
+
+- **Server-side only for gameplay.** A data pack is installed on the server, so every player of a room uses the same
+  content and the server can still check or recompute a battle. A player never installs gameplay content of their own.
+- **A content hash in the handshake** before data packs ship (`welcome`, `/healthz`, the BattleSpec), so a client and
+  a server can tell they run the same content, and a "modded" mark in the UI and in bug reports.
+- **No third-party code.** The manifest and its files are data (JSON, images, audio, fonts); a pack type that runs code
+  is a separate decision of the owner's.
+- **The golden results stay on the original content**; a pack never changes them.
+
+## 5. Tools
+
+```
+node tools/packs.mjs list [--json]          the packs by type, what was skipped and why, the warnings
+node tools/packs.mjs index [--out <file>]   write packs/index.json (the static index)
+node tools/packs.mjs check [--strict]       list; --strict exits 1 when a pack is skipped or warned about
+node tools/i18n.mjs template <code>         a new language pack (docs/I18N.md)
+node tools/i18n.mjs check <code> | --all    a language pack's strings: coverage, placeholders
+```
+
+`--root <dir>` points `tools/packs.mjs` at another checkout or an unpacked release.
+
+## 6. Shipping
+
+`tools/package.mjs` ships the committed packs (`public/i18n/`, `data/i18n/`, `packs/` — tracked files only: a pack
+installed on this machine and not committed stays out) and writes `packs/index.json` into the stage from the packs
+that ship. `test/package.test.js` checks both layouts and that a local pack stays out.
+
+## Tests
+
+`test/i18n-packs.test.js` (discovery of both layouts, broken / planned / duplicate packs, a pack dropped in or removed
+while the server runs, the file allowlist, the manifest and app ranges, the fallback chain, placeholders, plurals,
+the per-text game-text fallback, the client loader and menu, the tools, build-i18n `--lang` / `--dict`),
+`test/package.test.js`, `test/ui/i18n.e2e.test.js`
+(`SP_E2E=1`: a pack file and a pack folder dropped in while the server runs show in the menu and switch).
diff --git a/docs/history/0.2.0.md b/docs/history/0.2.0.md
index c986e7b3..38d9c61f 100644
--- a/docs/history/0.2.0.md
+++ b/docs/history/0.2.0.md
@@ -25,7 +25,8 @@ settled (泥岩's 闭锁; 忍冬, 深靛, 阿) → §25.11; release packaging an
 with no Spine model) → §25.12; round 18 — 拟态物质 at the copy cap (GitHub #207), 华法琳's 7 / 14 (GitHub #175, PR #192),
 a merged elite 拉普兰德 as a new one (GitHub #169), the leader pool per player alive (PR #209), the flying lift and two
 model quirks (PR #211) → §25.13; the community reports of 2026-10-06 (the 孤岛风云 prisoners drawn freed, 忍冬's trigger, a
-bounty burned to death by the 活性源石, 枯朽之种 paying a bounty) → §25.14.
+bounty burned to death by the 活性源石, 枯朽之种 paying a bounty) → §25.14; the rebindable shortcuts → §25.15; language packs,
+the first type of content packs (a language is a file in the language folder) → §25.16.
 
 Decisions of the owner: 2026-10-04 — the server stays on plain `node:http` + `ws`, no web framework (§25.1);
 2026-10-05 — the 补位 plan (§25.3); the 自选编队 rules, the collab operators out of the pool, ISW-A refused (§25.4);
@@ -38,7 +39,8 @@ a melee 突袭 member lands where it can block (§25.11); 华法琳's granted tr
 lock (§25.13.2); a newly merged elite 拉普兰德 counts as a new 拉普兰德 (§25.13.3); the leader pool = bloodPoint × the players
 alive at the fight's start, adopting PR #209 and replacing 「保持固定血量」 (§25.13.4); flying units at 1.3 tiles and the two
 model quirks of PR #211 (§25.13.5); the bounty pays whenever its enemy dies (relayed with the community
-reports, §25.14.3).
+reports, §25.14.3); 2026-10-07 — a language is a file in the language folder, and the language pack is the first type
+of a general content-pack mechanism (§25.16).
 
 ### 25.1 Refactor and tooling: the big files split, golden results, lint, types, import boundaries (refactor plan; owner's decision of 2026-10-04: no web framework) — `server/http/`, `server/match/match/`, `server/match/player/`, `server/sim/battle/`, `content/enemies/`, `kits/ops/`, `public/js/ui/gameLogic/`, `render/fx/`, `render/app/`, `screens/game/`, `tools/golden.mjs`, `tools/check-imports.mjs`, `eslint.config.js`, `jsconfig.json`
 
@@ -1092,3 +1094,63 @@ fixed (W5AA's commits name every golden scenario moved); two were already fixed
   `test/ui/gameLogic.test.js` (sanitizeSettings), `test/ui/hotkeys.e2e.test.js` (SP_E2E=1: 撤退 rebound to W with the
   keyboard only in the mock match — Q then does nothing, W retreats, the choice survives a reload; phone width). Docs:
   docs/PLAYING.md §11, README 操作, DESIGN §10 (design/client.md).
+
+### 25.16 Language packs: a language is a file in the language folder, the first type of content packs (W5AD; the owner's decisions of 2026-10-07) — `shared/packs.js`, `shared/i18nPacks.js`, `shared/i18n.js`, `shared/i18nData.js`, `server/packs.js`, `server/http/static.js`, `public/js/ui/lang.js`, `public/js/data.js`, `tools/i18n.mjs`, `tools/packs.mjs`, `tools/build-i18n.mjs`, `tools/package.mjs`, docs/I18N.md §5, docs/PACKS.md
+
+- **Seen**: after §25.2 English was wired in by name — the language list `['zh', 'en']`, the switch's labels, English
+  checks in the title screen, `fmtNum`, the tab title, a CSS rule, the overlay URL pattern — so another language meant
+  editing code, and players asked to translate into their own languages.
+- **Decision**: the owner's decision of 2026-10-07 — putting an adapted language file into the language folder is all
+  it takes for the game to offer that language, so the community can add languages themselves; the same day, design the
+  language pack as the first type of a general content-pack mechanism (later: resource packs for art / audio, then
+  server-side data packs) with one manifest, one registry and one index.
+- **Now** (docs/I18N.md §5 for translators, docs/PACKS.md for the mechanism):
+  - **A pack** is a manifest plus its files, in one of two layouts the same registry reads: the single file
+    `public/i18n/<code>.json` (manifest: its `_meta` block; optional game texts `data/i18n/<code>.json`) — the
+    translator's way and how English ships — or a folder `packs/<id>/pack.json` naming its files (every future type).
+    The manifest: type (`lang`; `assets` and `data` planned: parsed, listed as not supported, never served), version,
+    the app versions it targets (a range; outside it a language pack still loads and is flagged), its name in its own
+    language and in English, authors / credits / licence, and the type's fields (`lang`, `base`, `fallback`, `complete`,
+    `numberUnits`). English carries one like any pack (`complete: true`).
+  - **Discovery**: `server/packs.js` scans the language folders and `packs/` at start and again when their files
+    change (looked at on each index or pack-file request, at most once a second), validates the manifests, and answers
+    `GET /packs/index.json` (live, never cached; packs of supported types with the URLs of their files) and
+    `GET /packs/<id>/<file>` (only a file a manifest names, with its role's extension, inside the pack folder). A static
+    host uses `node tools/packs.mjs index` (packs/index.json); the release zips ship packs/ and that file. A broken
+    manifest, a planned type, a second pack for an id or a language: skipped with the reason in the server log and
+    `node tools/packs.mjs list`.
+  - **The client** lists every `lang` entry under its own name (title screen and 设置: buttons up to four languages, a
+    list beyond); `?lang=<code>` and the stored choice resolve to a listed pack (`en-US` → `en`; a pack that is gone →
+    Chinese); without an index the stored pack still loads by its code. Nothing in the client names English: the title
+    screen lays out by the script of the pack's title (`scriptOf`: an alphabetic title takes English's layout), the tab
+    title and `<html lang>` follow the pack, `fmtNum` takes `numberUnits` (Chinese 万 / 亿; without them K / M / B).
+  - **Fallback chain** per string: the pack → its base (`pt-BR` → `pt`; `zh-TW` none) → the packs `_meta.fallback`
+    names (English) → the Chinese msgid; game texts per text (each from the first overlay of the chain that has it:
+    `applyFileOverlay(json, overlay, onto)`, `data.setLocale(lang, chain)`).
+  - **Placeholders**: a translation that drops a plain placeholder of its msgid, uses one the caller does not pass, or
+    has a broken plural form is skipped like a missing one (the next language of the chain shows; a development page
+    warns once on the console; `tools/i18n.mjs check` checks the call sites). **Plurals**: `{n|one|other}` picks by
+    `Intl.PluralRules` (English exactly as before), and named categories serve other languages
+    (`{n|one:…|few:…|many:…|other:…}`).
+  - **Tools**: `node tools/i18n.mjs template <code>` (a skeleton: `_meta` and every msgid; on an existing pack only
+    the msgids it lacks), `check <code> | --all` (coverage; errors; a complete pack must have every msgid);
+    `node tools/build-i18n.mjs --lang ja | ko | zh-TW` builds a pack's game texts from the official JP / KR / TW client
+    (ArknightsAssets/ArknightsGamedata `jp/`, `kr/`, `tw/`, each with both 盟约 seasons, checked 2026-10-07: ja 96.5 %,
+    ko 97.4 %, zh-TW 91.1 % of 22 114 texts); a language without a client uses `--dict` (a community dictionary) or no
+    game texts at all (they follow the chain). No language but English ships: there is no Japanese, Korean or
+    Traditional Chinese UI pack yet, and a game-text file without its UI pack is not listed.
+- **The output in Chinese and English did not change**: `test/i18n-packs.test.js` renders every msgid of
+  `public/i18n/en.json` in both languages with sample params and compares it with the renderer of 0.2.0 before packs;
+  `node tools/build-i18n.mjs --check` still finds `data/i18n/en.json` up to date. One English entry was added, the tab
+  title (`卫戍协议：盟约 · STRONGHOLD PROTOCOL`, the same text as before).
+- [ASSUMED]: the menu turns into a list above four languages; two plain plural forms follow the language's rules (only
+  -1 renders differently from before in English, "-1 second"); a regional code falls back to its language's pack before
+  the declared fallbacks; with two packs for one language the language folder's file wins; a pack outside its app range
+  still loads; a development page is a dev build or one served from localhost.
+- Golden: unchanged. Tests: `test/i18n-packs.test.js` (12: discovery of both layouts and of broken / planned /
+  duplicate packs, a pack dropped in or removed while the server runs, the file allowlist, manifests and app ranges,
+  the chain, placeholders, plurals in English and Russian, the per-text game-text fallback, the client loader and menu,
+  the template / check / index tools, build-i18n's `--lang` and `--dict`, zh / en unchanged), `test/package.test.js` (both layouts ship, a local pack does
+  not, the generated index), `test/ui/i18n.e2e.test.js` (`SP_E2E=1`: a pack file and a pack folder dropped in while the
+  server runs show in the menu and switch, English filling the gaps; a removed pack sends the stored choice back to
+  Chinese); `test/i18n.test.js`, `test/i18n-data.test.js`, `test/i18n-server.test.js` unchanged and green.
diff --git a/shared/i18n.js b/shared/i18n.js
index db7beec4..e521abb9 100644
--- a/shared/i18n.js
+++ b/shared/i18n.js
@@ -3,9 +3,10 @@
 // The Chinese source string is the message id: `t('整备区已满')`, `t('还剩 {n} 秒', { n })`. A message without a
 // translation in the current language falls back to the Chinese text, so an untranslated string is never blank.
 // Chinese ('zh') is the default language; every other language is a pack (shared/i18nPacks.js): a file in
-// public/i18n/ that the client lists from /i18n/index.json and loads on demand (ui/lang.js). Nothing here knows a
-// language by name (the owner's decisions of 2026-10-05 and 2026-10-07: Chinese by default, a language is a file in the
-// language folder). docs/I18N.md explains how to add and translate strings and how to add a language.
+// public/i18n/ (or a pack folder, shared/packs.js) that the client lists from /packs/index.json and loads on demand
+// (ui/lang.js). Nothing here knows a language by name (the owner's decisions of 2026-10-05 and 2026-10-07: Chinese by
+// default, a language is a file in the language folder). docs/I18N.md explains how to add and translate strings and how
+// to add a language.
 //
 // Fallback chain per string: the chosen pack → its base (pt-BR → pt; zh-TW has none) → the packs its `_meta.fallback`
 // names (e.g. English) → the Chinese msgid (i18nPacks.js computeChain). A partial pack is fine: what it lacks falls
@@ -81,7 +82,7 @@ const notifyLangs = () => {
 };
 
 /**
- * Register languages (the client: the entries of /i18n/index.json; a pack's own `_meta` when it loads). A known code
+ * Register languages (the client: the language entries of /packs/index.json, shared/packs.js langMetaOf). A known code
  * is merged with what is there. Listeners of onLangsChange run once.
  * @param {Partial<LangMeta>[]} entries each with a `code`
  * @returns {number} languages registered
diff --git a/test/i18n-packs.test.js b/test/i18n-packs.test.js
index 6bcd2db7..5b23715f 100644
--- a/test/i18n-packs.test.js
+++ b/test/i18n-packs.test.js
@@ -21,7 +21,8 @@ import {
 } from '../shared/i18n.js';
 import { canonicalLang, computeChain, scriptOf, langFields } from '../shared/i18nPacks.js';
 import { normalizeManifest, appVersionMatches, isVersionRange, readPackIndex, langMetaOf, PACK_TYPES, isPackPath } from '../shared/packs.js';
-import { buildRecordOverlay, applyFileOverlay } from '../shared/i18nData.js';
+import { buildRecordOverlay, applyFileOverlay, applyRecordOverlay } from '../shared/i18nData.js';
+import { buildOverlay, LANG_SOURCES } from '../tools/build-i18n.mjs';
 import { scanPacks, createPackRegistry, packIndexOf } from '../server/packs.js';
 import { createDataStore } from '../public/js/data.js';
 import { checkPack, packTemplate } from '../tools/i18n.mjs';
@@ -389,3 +390,22 @@ test('tools: template writes a skeleton (or adds the missing msgids to a pack),
     assert.deepEqual(JSON.parse(fs.readFileSync(path.join(root, 'packs/index.json'), 'utf8')), body);
   } finally { fs.rmSync(root, { recursive: true, force: true }); }
 });
+
+test('build-i18n --lang: another official client (a text equal to the Chinese is no translation, no English composites); --dict for a language without one', () => {
+  assert.deepEqual(Object.keys(LANG_SOURCES), ['en', 'ja', 'ko', 'zh-TW']);
+  assert.match(LANG_SOURCES.ja.sources.assets.url, /ArknightsAssets\/ArknightsGamedata\/master\/jp\/gamedata\/$/);
+  const zh = [{ chars: { char_x: { name: '测试员', description: '攻击造成法术伤害' } } }];
+  const ja = [{ chars: { char_x: { name: 'テスター', description: '攻击造成法术伤害' } } }];
+  const data = { chess: { chess_x_a: { charId: 'char_x', name: '测试员', trait: { desc: '攻击造成法术伤害' } } }, stages: { m1: { name: '战场#05(下半) 测试员' } } };
+  const { overlay, report } = buildOverlay({ zh, en: ja, data, lang: 'ja' });
+  assert.equal(overlay.lang, 'ja');
+  const c = applyRecordOverlay(data.chess.chess_x_a, overlay.files.chess.chess_x_a).value;
+  assert.deepEqual([c.name, c.trait.desc], ['テスター', '攻击造成法术伤害'], 'the JP text equal to the Chinese one stays untranslated (falls back at run time)');
+  assert.equal(overlay.files.stages, undefined, 'the remake\'s stage-name composite is English wording only');
+  assert.equal(overlay.names['测试员'], 'テスター');
+  assert.equal(report.coverage.operators.translated, 1);
+  const fr = buildOverlay({ zh: [], en: [], data, lang: 'fr', fallback: { dict: { 测试员: 'Testeur', 攻击造成法术伤害: 'Inflige des dégâts magiques' } } });
+  const f = applyRecordOverlay(data.chess.chess_x_a, fr.overlay.files.chess.chess_x_a).value;
+  assert.deepEqual([fr.overlay.lang, f.name, f.trait.desc, fr.overlay.names['测试员']], ['fr', 'Testeur', 'Inflige des dégâts magiques', 'Testeur']);
+  assert.deepEqual([fr.report.coverage.operators.dict, fr.report.coverage.traits.dict], [1, 1], 'counted as the dictionary\'s');
+});
diff --git a/test/ui/i18n.e2e.test.js b/test/ui/i18n.e2e.test.js
index f75e3d0f..2c41ed7e 100644
--- a/test/ui/i18n.e2e.test.js
+++ b/test/ui/i18n.e2e.test.js
@@ -4,15 +4,25 @@
 //
 // The title screen opens in Chinese; 中文 | English → English in place (no reload): the title, the start button, the
 // connection line, <html lang>, the tab title; the choice is kept across a reload (localStorage sp.pref.lang) and the
-// game-data overlay (data/i18n/en.json) is applied; `?lang=zh` switches back and leaves the address bar. No console /
-// page / request errors. docs/I18N.md.
+// game-data overlay (data/i18n/en.json) is applied; `?lang=zh` switches back and leaves the address bar. Language packs
+// (docs/I18N.md "Adding a language", docs/PACKS.md): a pack file dropped into public/i18n/ and a pack folder dropped
+// into packs/ while the server runs show in the menu and switch, with English filling what they lack; a removed pack
+// sends a stored choice back to Chinese. No console / page / request errors. docs/I18N.md.
 
 import { test, describe, before, after } from 'node:test';
 import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
 import { CHROME, hasChrome, sleep } from '../e2e/client.mjs';
 import { NAME_MAX_LEN } from '../../shared/constants.js';
 
 const ENABLED = process.env.SP_E2E === '1' && hasChrome();
+const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '../..');
+// example packs, only for this test ('qaa' … 'qtz' are the ISO 639 codes reserved for local use); removed afterwards
+const PACK_FILE = path.join(ROOT, 'public/i18n/qaa.json');
+const PACK_DIR = path.join(ROOT, 'packs/qab');
+const removePacks = () => { fs.rmSync(PACK_FILE, { force: true }); fs.rmSync(PACK_DIR, { recursive: true, force: true }); };
 
 describe('language switch on the title screen', { skip: !ENABLED && 'set SP_E2E=1 (Chrome)' }, () => {
   let srv;
@@ -25,7 +35,7 @@ describe('language switch on the title screen', { skip: !ENABLED && 'set SP_E2E=
     base = `http://127.0.0.1:${srv.port}`;
     browser = await puppeteer.launch({ executablePath: CHROME, headless: true, args: ['--no-sandbox', '--force-device-scale-factor=1'] });
   });
-  after(async () => { await browser?.close(); await srv?.close(); });
+  after(async () => { removePacks(); await browser?.close(); await srv?.close(); });
 
   const text = (page, sel) => page.$eval(sel, (el) => el.textContent.replace(/\s+/g, ' ').trim());
 
@@ -69,4 +79,50 @@ describe('language switch on the title screen', { skip: !ENABLED && 'set SP_E2E=
     assert.deepEqual(problems, []);
     await page.close();
   });
+  test('a pack dropped into the language folder or into packs/ shows in the menu and switches; English fills its gaps', async () => {
+    const page = await browser.newPage();
+    await page.setViewport({ width: 1600, height: 900 });
+    const problems = [];
+    page.on('console', (m) => { if (m.type() === 'error') problems.push(`console: ${m.text()}`); });
+    page.on('pageerror', (e) => problems.push(`pageerror: ${e.message}`));
+    page.on('response', (r) => { if (r.status() >= 400 && !/fonts\.(googleapis|gstatic)/.test(r.url())) problems.push(`http ${r.status()}: ${r.url()}`); });
+    try {
+      fs.writeFileSync(PACK_FILE, JSON.stringify({ _meta: { name: 'Testisch', englishName: 'Test language', fallback: ['en'] }, 卫戍协议: 'Testprotokoll', 盟约: 'Bund', 开始: 'Los' }));
+      fs.mkdirSync(PACK_DIR, { recursive: true });
+      fs.writeFileSync(path.join(PACK_DIR, 'pack.json'), JSON.stringify({ type: 'lang', lang: 'qab', name: 'Qabisch', files: { ui: 'ui.json' } }));
+      fs.writeFileSync(path.join(PACK_DIR, 'ui.json'), JSON.stringify({ 开始: 'Qab-Start' }));
+      await sleep(1100); // the server's registry looks at the folders again after a second
+      await page.goto(`${base}/?lang=zh`, { waitUntil: 'networkidle0' });
+      await page.waitForSelector('.title-screen [data-testid="lang-toggle"] button[data-lang="qaa"]');
+      assert.deepEqual(await page.$$eval('[data-testid="lang-toggle"] button', (bs) => bs.map((b) => [b.dataset.lang, b.textContent.trim()])),
+        [['zh', '中文'], ['en', 'English'], ['qaa', 'Testisch'], ['qab', 'Qabisch']]);
+
+      await page.click('[data-testid="lang-toggle"] button[data-lang="qaa"]');
+      await page.waitForFunction(() => document.querySelector('.title-login .btn--primary')?.textContent.includes('Los'), { timeout: 8000 });
+      assert.equal(await text(page, '.title-cn'), 'Testprotokoll: Bund', 'an alphabetic title: the display face, an ASCII colon');
+      assert.match(await text(page, '.title-tag'), /^Allocate Funds and Operators/, 'untranslated: English, the pack\'s fallback');
+      assert.deepEqual(await page.evaluate(() => ({ lang: document.documentElement.lang, script: document.documentElement.dataset.script, pref: localStorage.getItem('sp.pref.lang') })),
+        { lang: 'qaa', script: 'alphabetic', pref: '"qaa"' });
+      // no game texts of its own: English's through the chain
+      await page.waitForFunction(() => globalThis.__SP__?.data?.locale() === 'qaa', { timeout: 8000 });
+      assert.equal(await page.evaluate(() => globalThis.__SP__.data.get('config').modes.mode_multi_abyss.name), 'Ultimate Simulation');
+
+      await page.click('[data-testid="lang-toggle"] button[data-lang="qab"]');
+      await page.waitForFunction(() => document.querySelector('.title-login .btn--primary')?.textContent.includes('Qab-Start'), { timeout: 8000 });
+      assert.equal(await text(page, '.title-cn'), '卫戍协议：盟约', 'no fallback declared: the Chinese msgid');
+
+      await page.click('[data-testid="lang-toggle"] button[data-lang="qaa"]');
+      await page.waitForFunction(() => document.querySelector('.title-login .btn--primary')?.textContent.includes('Los'), { timeout: 8000 });
+      removePacks();
+      await sleep(1100);
+      await page.reload({ waitUntil: 'networkidle0' });
+      await page.waitForSelector('.title-screen .title-cn');
+      assert.equal(await text(page, '.title-cn'), '卫戍协议：盟约', 'the stored pack is gone: Chinese');
+      assert.deepEqual(await page.$$eval('[data-testid="lang-toggle"] button', (bs) => bs.map((b) => b.dataset.lang)), ['zh', 'en']);
+      assert.deepEqual(problems, []);
+    } finally {
+      removePacks();
+      await page.close();
+    }
+  });
 });
diff --git a/tools/build-i18n.mjs b/tools/build-i18n.mjs
index 777e540f..920a0a8c 100644
--- a/tools/build-i18n.mjs
+++ b/tools/build-i18n.mjs
@@ -27,9 +27,10 @@
 //   --lang      the target language (default en): one with an official client in LANG_SOURCES — en, ja (the JP
 //               client), ko (KR), zh-TW (TW); all three carry both 盟约 seasons (verified 2026-10-07, data 51.x). The
 //               output goes to data/i18n/<code>.json, the game texts of the language pack <code> (it needs the pack's
-//               UI file public/i18n/<code>.json to show in the menu). A language with no official client gets its game
-//               texts another way (docs/I18N.md): the pack's UI file fills the data texts equal to one of its msgids,
-//               the rest falls back per text (the pack's chain, then Chinese).
+//               UI file public/i18n/<code>.json to show in the menu). Any other code needs --dict.
+//   --dict      a community dictionary { "<Chinese data text>": "<translation>" } (a language without an official
+//               client: the only source besides the pack's UI file; with a client: tried after it). Matching is exact
+//               (a text with its numbers resolved needs its own entry); the rest falls back per text at run time.
 //   --source    tables of the language: 'assets' (default) = ArknightsAssets/ArknightsGamedata (en / jp / kr / tw;
 //               current, has the 盟约 seasons act1autochess / act2autochess); for en also 'yostar' =
 //               Kengxxiao/ArknightsGameData_YoStar en_US (archived in 2025-11: no 盟约 season, only the 2025 test event
@@ -47,12 +48,12 @@
 
 import { mkdir, readFile, writeFile, rename } from 'node:fs/promises';
 import { existsSync } from 'node:fs';
-import { dirname, join, resolve, relative } from 'node:path';
+import { basename, dirname, join, resolve, relative } from 'node:path';
 import { fileURLToPath } from 'node:url';
 import { buildRecordOverlay, applyFileOverlay, OVERLAY_VERSION } from '../shared/i18nData.js';
 
 const ROOT = resolve(dirname(fileURLToPath(import.meta.url)), '..');
-const USAGE = 'usage: node tools/build-i18n.mjs [--lang en|ja|ko|zh-TW] [--refresh | --offline] [--source assets|yostar] [--cache <dir>] [--cache-en <dir>] [--data <dir>] [--out <file>] [--report <file>] [--check] [--quiet]';
+const USAGE = 'usage: node tools/build-i18n.mjs [--lang en|ja|ko|zh-TW | --lang <code> --dict <file.json>] [--dict <file.json>] [--refresh | --offline] [--source assets|yostar] [--cache <dir>] [--cache-en <dir>] [--data <dir>] [--out <file>] [--report <file>] [--check] [--quiet]';
 
 const ASSETS_HOME = 'https://github.com/ArknightsAssets/ArknightsGamedata';
 /** The official client tables of a language other than English (ArknightsAssets/ArknightsGamedata <server>/gamedata). */
@@ -92,7 +93,7 @@ export const LANG_SOURCES = Object.freeze({
 });
 
 /** The test "this target text is no translation of that Chinese one" of a language (LANG_SOURCES `untranslated`). */
-const untranslatedTest = (lang) => (LANG_SOURCES[lang]?.untranslated === 'same' ? (zh, t) => t === zh : (zh, t) => hasCjk(t));
+const untranslatedTest = (lang) => ((LANG_SOURCES[lang]?.untranslated ?? 'same') === 'same' ? (zh, t) => t === zh : (zh, t) => hasCjk(t));
 
 /** Official tables walked side by side (zh_CN ↔ EN), with the sub-trees that hold texts the remake uses. */
 const TABLES = [
@@ -190,7 +191,7 @@ function parseArgs(argv) {
     cache: join(ROOT, '.cache', 'gamedata'), cacheEn: null, data: join(ROOT, 'data'), out: null, report: null,
   };
   const flags = { '--refresh': 'refresh', '--offline': 'offline', '--quiet': 'quiet', '--check': 'check' };
-  const vals = { '--source': 'source', '--lang': 'lang', '--cache': 'cache', '--cache-en': 'cacheEn', '--data': 'data', '--out': 'out', '--report': 'report' };
+  const vals = { '--source': 'source', '--lang': 'lang', '--dict': 'dict', '--cache': 'cache', '--cache-en': 'cacheEn', '--data': 'data', '--out': 'out', '--report': 'report' };
   for (let i = 0; i < argv.length; i++) {
     const eq = argv[i].indexOf('=');
     const [name, inline] = eq > 0 ? [argv[i].slice(0, eq), argv[i].slice(eq + 1)] : [argv[i], null];
@@ -206,9 +207,10 @@ function parseArgs(argv) {
   }
   if (opts.refresh && opts.offline) throw new Error(`--refresh and --offline are mutually exclusive\n${USAGE}`);
   const lang = LANG_SOURCES[opts.lang];
-  if (!lang) throw new Error(`--lang must be one of ${Object.keys(LANG_SOURCES).join(', ')} (a language with an official client; docs/I18N.md says how a pack without one gets its game texts)`);
-  if (!lang.sources[opts.source]) throw new Error(`--source for ${opts.lang} must be one of ${Object.keys(lang.sources).join(', ')}`);
-  if (!opts.cacheEn) opts.cacheEn = join(ROOT, lang.sources[opts.source].cache);
+  if (!/^[a-z]{2,3}(?:-[A-Za-z0-9]{2,8})*$/.test(opts.lang) || opts.lang === 'zh') throw new Error(`--lang ${opts.lang}: a language code (en, ja, zh-TW …; not zh, the source)`);
+  if (!lang && !opts.dict) throw new Error(`--lang ${opts.lang} has no official client here (${Object.keys(LANG_SOURCES).join(', ')}): give its game texts with --dict <file.json> (docs/I18N.md §2)`);
+  if (lang && !lang.sources[opts.source]) throw new Error(`--source for ${opts.lang} must be one of ${Object.keys(lang.sources).join(', ')}`);
+  if (!opts.cacheEn && lang) opts.cacheEn = join(ROOT, lang.sources[opts.source].cache);
   if (!opts.out) opts.out = join(ROOT, 'data', 'i18n', `${opts.lang}.json`);
   if (!opts.report) opts.report = join(ROOT, '.cache', opts.lang === 'en' ? 'build-i18n-report.json' : `build-i18n-report.${opts.lang}.json`);
   return opts;
@@ -596,7 +598,7 @@ function translateScalar(file, id, text, tr, stats, samples) {
 
 class Stats {
   constructor() { this.kinds = {}; this.missing = new Map(); }
-  row(kind) { return this.kinds[kind] || (this.kinds[kind] = { texts: 0, exact: 0, template: 0, composite: 0, remake: 0, pr70: 0, ui: 0, missing: 0, notes: 0 }); }
+  row(kind) { return this.kinds[kind] || (this.kinds[kind] = { texts: 0, exact: 0, template: 0, composite: 0, remake: 0, pr70: 0, ui: 0, dict: 0, missing: 0, notes: 0 }); }
   hit(kind, how) { const r = this.row(kind); r.texts++; r[how]++; }
   miss(kind, text) {
     const r = this.row(kind);
@@ -623,6 +625,7 @@ export function buildOverlay({ zh, en, data, fallback = {}, source = null, lang
   const index = new PairIndex(untranslated);
   for (let i = 0; i < zh.length; i++) index.walk(zh[i], en[i], []);
   const tr = new Translator(index, [
+    ...(fallback.dict ? [{ name: 'dict', map: dictMap(fallback.dict, untranslated) }] : []),
     { name: 'remake', map: dictMap(fallback.remake, untranslated) },
     { name: 'pr70', map: dictMap(fallback.pr70, untranslated) },
     { name: 'ui', map: dictMap(fallback.ui, untranslated) },
@@ -664,7 +667,7 @@ export function buildOverlay({ zh, en, data, fallback = {}, source = null, lang
   const coverage = {};
   let total = 0, translated = 0, official = 0;
   for (const [kind, r] of Object.entries(stats.kinds).sort()) {
-    const ok = r.exact + r.template + r.composite + r.remake + r.pr70 + r.ui;
+    const ok = r.exact + r.template + r.composite + r.remake + r.pr70 + r.ui + r.dict;
     coverage[kind] = { ...r, translated: ok, pct: r.texts ? Math.round((ok / r.texts) * 1000) / 10 : 100 };
     total += r.texts; translated += ok; official += r.exact + r.template + r.composite;
   }
@@ -692,11 +695,13 @@ async function main() {
   let opts;
   try { opts = parseArgs(process.argv.slice(2)); } catch (e) { console.error(`build-i18n: ${e.message}`); process.exit(2); }
   const log = (...a) => { if (!opts.quiet) console.log(...a); };
-  const src = LANG_SOURCES[opts.lang].sources[opts.source];
+  const client = LANG_SOURCES[opts.lang];
+  // (the dictionary by its file name only: a path outside the repository must not end up in the output)
+  const src = client ? client.sources[opts.source] : { label: `the dictionary ${basename(opts.dict)}`, home: null, url: null };
   log(`build-i18n: ${opts.lang} tables from ${src.label}`);
   const zh = [];
   const en = [];
-  for (const t of TABLES) {
+  for (const t of client ? TABLES : []) {
     const zj = await loadTable(opts.cache, ZH_URL, t.rel, { refresh: false, offline: opts.offline, log });
     const ej = await loadTable(opts.cacheEn, src.url, t.rel, { refresh: opts.refresh, offline: opts.offline, log });
     zh.push(t.pick ? t.pick(zj) : zj);
@@ -704,14 +709,14 @@ async function main() {
   }
   const seasonEn = en[0]?.act2 ? 'act2autochess' : en[0]?.act1 ? 'act1autochess' : 'none (no 盟约 season in this EN build)';
   let version = null;
-  const versionFile = join(opts.cacheEn, 'excel', 'data_version.txt');
-  if (!opts.offline && (opts.refresh || !existsSync(versionFile))) {
+  const versionFile = client ? join(opts.cacheEn, 'excel', 'data_version.txt') : '';
+  if (client && !opts.offline && (opts.refresh || !existsSync(versionFile))) {
     try {
       const res = await fetch(`${src.url}excel/data_version.txt`, { signal: AbortSignal.timeout(30_000) });
       if (res.ok) { await mkdir(dirname(versionFile), { recursive: true }); await writeFile(versionFile, await res.text()); }
     } catch { /* optional */ }
   }
-  try { version = (await readFile(versionFile, 'utf8')).trim(); } catch { /* optional */ }
+  try { version = versionFile ? (await readFile(versionFile, 'utf8')).trim() : null; } catch { /* optional */ }
   const data = {};
   for (const f of DATA_FILES) {
     const abs = join(opts.data, `${f}.json`);
@@ -724,7 +729,8 @@ async function main() {
     pr70: await readDict(join(ROOT, 'tools', 'i18n', 'fallback-pr70.json')),
     ui: await readDict(join(ROOT, 'public', 'i18n', 'en.json')),
   } : { ui: await readDict(join(ROOT, 'public', 'i18n', `${opts.lang}.json`)) };
-  const { overlay, report } = buildOverlay({ zh, en, data, fallback, lang: opts.lang, source: { id: opts.source, label: src.label, home: src.home, season: seasonEn } });
+  if (opts.dict) fallback.dict = JSON.parse(await readFile(opts.dict, 'utf8'));
+  const { overlay, report } = buildOverlay({ zh, en, data, fallback, lang: opts.lang, source: client ? { id: opts.source, label: src.label, home: src.home, season: seasonEn } : { id: 'dict', label: src.label } });
 
   // self-check: applying the overlay keeps every record's shape (strings replace strings only)
   let applied = 0;
@@ -737,10 +743,10 @@ async function main() {
   const rep = { ...report, source: overlay.meta.source, enDataVersion: version, applied, bytes: Buffer.byteLength(text) };
   await mkdir(dirname(opts.report), { recursive: true });
   await writeFile(opts.report, `${JSON.stringify(rep, null, 1)}\n`);
-  log(`  season in the ${opts.lang} build: ${seasonEn}${version ? ` · ${version.replace(/\s+/g, ' ')}` : ''}`);
+  if (client) log(`  season in the ${opts.lang} build: ${seasonEn}${version ? ` · ${version.replace(/\s+/g, ' ')}` : ''}`);
   log(`  ${report.pairs} zh→${opts.lang} source pairs; coverage per kind (translated / texts):`);
   for (const [kind, c] of Object.entries(report.coverage)) {
-    const fb = [c.remake && `remake ${c.remake}`, c.pr70 && `PR #70 ${c.pr70}`, c.ui && `UI ${c.ui}`].filter(Boolean).join(' · ');
+    const fb = [c.remake && `remake ${c.remake}`, c.pr70 && `PR #70 ${c.pr70}`, c.ui && `UI ${c.ui}`, c.dict && `dictionary ${c.dict}`].filter(Boolean).join(' · ');
     log(`    ${kind.padEnd(10)} ${String(c.translated).padStart(5)} / ${String(c.texts).padEnd(5)} ${String(c.pct).padStart(5)} %   official ${c.exact + c.template + c.composite} (exact ${c.exact} · template ${c.template} · composite ${c.composite})${fb ? ` · ${fb}` : ''}${c.notes ? ` · notes skipped ${c.notes}` : ''}`);
   }
   log(`  total ${report.totals.translated} / ${report.totals.texts} (${report.totals.pct} %), official ${report.totals.official}; ${Object.keys(overlay.names).length} names (${report.nameConflicts.length} with several ${opts.lang} forms)`);