fix: fall back to original language on post redirect

.unipi/docs/fix/2026-06-04-favorite-other-language-post-redirect-fix.md

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+---
+title: "Favorite Other-Language Post Redirect — Quick Fix"
+type: quick-fix
+date: 2026-06-04
+---
+
+# Favorite Other-Language Post Redirect — Quick Fix
+
+## Bug
+
+When the user is on a UI language (e.g. Chinese) and clicks a favorited post that does not have a translation in that language, the post page silently redirected to `/browse` and the user could not see the post.
+
+## Root Cause
+
+`src/pages/PostRedirect/index.tsx` requested `GET /api/posts/{id}?lang=<ui-lang>`. The backend returns `404` when the post has no translation in the requested language. The redirect's `.catch` silently sent the user to `/browse`, hiding the post entirely.
+
+## Fix
+
+`PostRedirect` now retries without the `lang` parameter on failure. If the post exists in any language, the user is taken to the post anyway, and a toast tells them the post is shown in its original language because the selected language is unavailable. If the retry also fails (post truly missing), behavior is unchanged: redirect to `/browse`.
+
+A new i18n key `postShownInOriginalLanguage` was added in all 7 locales.
+
+### Files Modified
+
+- `src/pages/PostRedirect/index.tsx` — added language fallback fetch, toast notice.
+- `src/locales/zh-CN.ts` — added `postShownInOriginalLanguage`.
+- `src/locales/en.ts` — added `postShownInOriginalLanguage`.
+- `src/locales/ja.ts` — added `postShownInOriginalLanguage`.
+- `src/locales/ko.ts` — added `postShownInOriginalLanguage`.
+- `src/locales/vi.ts` — added `postShownInOriginalLanguage`.
+- `src/locales/id.ts` — added `postShownInOriginalLanguage`.
+- `src/locales/ms.ts` — added `postShownInOriginalLanguage`.
+
+## Verification
+
+- `npx tsc --noEmit`
+- `npm run format:check`
+- `npm test` (13 files, 49 tests)
+- Staging curl confirmed: `GET /api/posts/{id}?lang=en` returns `404` for a Chinese-only post, while `GET /api/posts/{id}` returns `200` with the post in its source language.
+
+## Notes
+
+No deploy was performed.