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# Dashboard i18n Guide
Last Updated: 2026-03-02
This document describes the internationalization (i18n) architecture used by the CCS Dashboard (`ui/`), how locale selection works, and how to add new languages safely.
---
## Scope
Dashboard i18n currently covers UI text rendered by React components.
- Supported locales today:
- `en` (English)
- `zh-CN` (Simplified Chinese)
- `vi` (Vietnamese)
- Locale state is persisted in browser localStorage using `ccs-ui-locale`.
- Fallback language is `en`.
Out of scope:
- CLI terminal output localization
- Backend/API payload localization
---
## Architecture
### Initialization
- File: `ui/src/App.tsx`
- `import '@/lib/i18n'` initializes i18next once before routes render.
### Translation resources
- File: `ui/src/lib/i18n.ts`
- Contains `resources` object with locale blocks:
- `en.translation`
- `zh-CN.translation`
- `vi.translation`
- Uses `initReactI18next` for React integration.
### Locale utilities
- File: `ui/src/lib/locales.ts`
- Core helpers:
- `normalizeLocale(locale)` maps browser/storage values to supported app locales.
- `getInitialLocale` chooses stored locale, then browser locale, then `en`.
- `persistLocale` writes normalized locale to localStorage.
### Language switcher
- File: `ui/src/components/layout/language-switcher.tsx`
- Uses `react-i18next` + shadcn `Select`.
- Calls `persistLocale` and `i18n.changeLanguage` on selection.
---
## Key Conventions
### Translation key naming
Use dot-notation namespaces by feature area:
- `nav.home`
- `cursorPage.title`
- `settingsTabs.web`
Keep key names stable and semantic to minimize churn across locales.
### Pluralization
For count-based strings, use i18next suffix rules:
- `<key>_one`
- `<key>_other`
Examples exist in sync/account counters.
### Interpolation and rich text
- Use interpolation for runtime values: `t('key', { value })`.
- Prefer plain text keys whenever possible.
- If formatting is required (for example bold segments), use `<Trans />` instead of `dangerouslySetInnerHTML`.
---
## Adding a New Locale
When adding a locale such as Thai (`th`):
1. Add locale id to the supported locale list in `ui/src/lib/locales.ts`.
2. Add locale display label under `translation.locale` in `ui/src/lib/i18n.ts`.
3. Add a full `<locale>.translation` block with all keys.
4. Verify fallback behavior remains `en` for missing keys.
5. Run UI validation and i18n tests:
- `cd ui && bun run validate`
- `cd ui && bun run test:run tests/unit/ui/i18n/language-switcher.test.tsx`
6. Add or update key-parity tests to catch locale drift.
Current issue driving the Vietnamese rollout:
- https://github.com/kaitranntt/ccs/issues/659
---
## Contributor Checklist
Before opening a PR that touches i18n:
- [ ] New UI strings are translated in all supported locales.
- [ ] No raw key literals appear in UI at runtime.
- [ ] No unsafe HTML injection path introduced for translated content.
- [ ] `ui` validate/test commands pass.
- [ ] This document is updated if architecture or conventions changed.