Locale UI Patterns

Core Rule

User-facing UI text must go through @/lib/i18n; do not hardcode English strings in components.

Translate everything immediately (no English placeholders)

Every key you add to a non-English dictionary MUST contain a real translation in that language — never the English source string as a stand-in. There is NO "leave it in English for now" convention in this project; if an agent told you there was, it was wrong. Copying the English value into es.ts/fr.ts/ko.ts/pl.ts/pt-BR.ts/uk.ts/zh-CN.ts/zh-TW.ts is a defect, not a deferral. The app ships every locale at once, so an untranslated key is a visible bug for those users.

If you genuinely cannot translate a language, say so explicitly to the user instead of silently pasting English. Do not invent a fallback policy.

Required Flow

1. Add or reuse a key in packages/ui/src/lib/i18n/messages/en.ts.
2. Add the same key — fully translated, not the English text — to every non-English dictionary in packages/ui/src/lib/i18n/messages/.
3. In components, call const { t } = useI18n() from @/lib/i18n and render t('key').
4. For locale names or language picker labels, use label(locale) from useI18n().
5. Keep locale state in packages/ui/src/lib/i18n/*; do not add locale fields to broad stores like useUIStore.
6. Do not remount the app to update language. Components must re-render through useI18n().

Component Usage Rules

• Import from @/lib/i18n, not deep files.
• Keep t(...) calls inside React render/hook scope so locale changes re-render text.
• Do not resolve translated text at module scope.
• For static option arrays, store labelKey / descriptionKey; resolve with t(...) inside the component.
• For non-React helpers, pass translated strings in from the component or pass t explicitly.

Key Style

Use stable semantic keys, not English text as keys.

Keys should describe location + UI role + meaning. They should not encode current copy wording.

Use existing nearby naming when extending a surface. If no nearby pattern exists, choose a short path that mirrors the UI ownership.

Namespaces like layout.*, settings.*, chat.*, git.*, session.*, toast.*, and dialog.* are examples, not a fixed exhaustive list.

Good:

'settings.appearance.language.label': 'Language'
'layout.mainTab.chat': 'Chat'
'chat.input.placeholder': 'Ask OpenChamber...'

Bad:

'Language': 'Language'
'chatLabel': 'Chat'
'askOpenChamberDotDotDot': 'Ask OpenChamber...'

Avoid overly generic keys unless the text is truly global and context-independent. Prefer specific keys when button meaning can vary by surface.

Parameters

Use {name} placeholders for dynamic values.

'toast.language.changed': 'Language changed to {language}'

t('toast.language.changed', { language: label(locale) })

Do not pass grammar fragments as params. Never use params like {suffix}, {plural}, {article}, {prefix}, {dateSuffix}, or pieces of words/sentences.

Bad:

t('dialog.delete.description', { count, suffix: count === 1 ? '' : 's' })

Good:

count === 1
  ? t('dialog.delete.descriptionSingle', { count })
  : t('dialog.delete.descriptionPlural', { count })

Plural/count-dependent text must use separate complete-message keys unless all supported locales can use one identical complete sentence. Placeholders are only for real values ({count}, {name}, {path}), not grammar.

Optional clauses must also be complete-message keys. Do not build a sentence by injecting a translated phrase into another translated sentence.

Bad:

t('dialog.delete.description', {
  dateLabel: date ? t('dialog.delete.dateSuffix', { date }) : '',
})

Good:

date
  ? t('dialog.delete.descriptionWithDate', { count, date })
  : t('dialog.delete.description', { count })

Translation Boundary

Translate visible text, placeholders, tooltips, dialogs, toasts, empty/error/loading states, and user-facing aria-label, title, and alt text.

Keep these literal:

• Product names: OpenChamber, OpenCode, GitHub
• Protocol/tool acronyms: MCP, SSE, WebSocket, API
• Model/provider names
• File paths, command names, environment variables
• User/generated content

Completion Criteria

• No new hardcoded user-facing English in changed UI files.
• Every new key exists in all dictionaries with a real translation.
• All translated values are resolved inside a reactive render/hook boundary.
• No locale state added to broad/shared stores.
• No full app remount for locale changes.
• Locale switch preserves current UI state.