feedback5 WI: docs/I18N.md (translating, adding strings, rebuilding the EN game texts, phase 2) and credits

NOTICE.md and THIRD-PARTY-NOTICES.md credit @YuriRestia (PR #70) for the English UI strings and fallback
translations, note that PR #70's ak-spa-database.pages.dev texts are not used and that arknights.wiki.gg is
CC BY-SA 4.0, and name the EN data mirrors (ArknightsAssets/ArknightsGamedata, Kengxxiao/ArknightsGameData_YoStar).
DATA.md: data/i18n/en.json is written by tools/build-i18n.mjs (rerun after a text-changing build).
PLAYING.md: the 中文 / English switch.

THIRD-PARTY-NOTICES.md

@@ -48,9 +48,22 @@ All names, characters, artwork, Spine models, UI graphics, music, sound effects
 [fexli/ArknightsResource](https://github.com/fexli/ArknightsResource),
 [isHarryh/Ark-Models](https://github.com/isHarryh/Ark-Models),
 [ArknightsAssets/ArknightsAssets2](https://github.com/ArknightsAssets/ArknightsAssets2) — thanks to their maintainers.
+The English game texts (`data/i18n/en.json`, `tools/build-i18n.mjs`) come from the official EN client tables mirrored by
+[ArknightsAssets/ArknightsGamedata](https://github.com/ArknightsAssets/ArknightsGamedata) (`en/gamedata`, the default
+source) and [Kengxxiao/ArknightsGameData_YoStar](https://github.com/Kengxxiao/ArknightsGameData_YoStar) (`en_US`,
+`--source yostar`); same terms as the rest of the game data.
 Quotations of PRTS Wiki, BWIKI, NGA, 巴哈姆特 and other community pages in `docs/` stay under the terms of their
 sources (the wikis' texts are CC BY-NC-SA).
 
+## Translations
+
+The English UI strings (`public/i18n/en.json`) and the fallback game-text translations (`tools/i18n/fallback-pr70.json`)
+are based on GitHub PR #70 (branch `en-translation`) by **@YuriRestia**, reused with credit and released with the project
+under GPL-3.0-or-later (docs/I18N.md). PR #70 named ak-spa-database.pages.dev and arknights.wiki.gg as references: texts
+it took from ak-spa-database.pages.dev (no licence) are excluded; arknights.wiki.gg is CC BY-SA 4.0, which may be combined
+into a GPL-3.0 work (the one-way compatibility Creative Commons declared) — thanks to its contributors. Official game
+terms and names in those files remain © Hypergryph / Yostar.
+
 ---
 
 ## Licence texts