Applied as-is. initLang and switchLang record a request counter before the first await and apply a pack only when that request is still the latest. Choosing the language already on screen cancels an in-flight load. A failed latest choice still saves the preference and leaves the previous UI.
Tests: node --test test/ui/lang.test.js test/ui/i18n.e2e.test.js test/i18n-packs.test.js test/i18n-server.test.js — 29 pass, 0 fail. The Chrome suite in test/ui/i18n.e2e.test.js skipped (SP_E2E unset).
public/i18n/en.json: Chinese msgid -> English, seeded from PR #70 (@YuriRestia, credited) for every Chinese
literal of the current code (≈830 entries; 966 of the 1 036 literals left for phase 2 already translated),
completed by hand in the official EN terms. public/js/ui/lang.js: boot language (?lang=en|zh, then
localStorage sp.pref.lang, else Chinese; the browser language is not consulted), switchLang, useLang,
LangToggle; main.js renders after initLang and re-renders in place on a switch, and translates server
texts (m.toast / m.ticker frames, room.closed reasons, error codes via ui/toasts.js describeError).
Converted: title screen (English title, wordmark hidden), lobby, room, settings (语言 row, On/Off,
quality, hotkeys), the shell (crash screen, toasts) and DifficultyTag.
tools/i18n.mjs: extract (msgids + untranslated literals per file), check (msgids missing from en.json),
codemod (html`` text / attributes / strings / template literals -> t(), nested strings, N_ for module
level, i18n-ignore lines), seed (fill en.json from a msgid map).
siruimei07