Internationalization — opt-in translations

English (en-US) is the default source locale. Do not create or update additional locale catalogs unless the app's agent-native.config.ts lists them under translations.locales.

Rule

Visible framework/template UI copy belongs in the app's i18n catalog, not inline in components. When you add or edit UI text, update the English source catalog first, then update only the locale catalogs listed in translations.locales, and run the i18n guard.

Catalogs

Templates use app/i18n/:

• en-US.ts is the canonical source tree and fallback.
• Other locale files keep the same non-plural keys and the same placeholders.
• index.ts exports an AgentNativeI18nCatalog with English bundled and non-English catalogs loaded by dynamic import.

Use BCP-47 filenames from the supported set: en-US, zh-CN, es-ES, fr-FR, de-DE, ja-JP, ko-KR, pt-BR, hi-IN, ar-SA.

If an app only ships translations for a subset of that set, set supportedLocales on the AgentNativeI18nCatalog to that subset. Without it, <LanguagePicker /> lists every framework-supported locale regardless of whether loadMessages can actually resolve it.

UI Pattern

• Wrap apps with AppProviders i18n={{ catalog: i18nCatalog }}.
• Read strings with useT() and keep keys stable.
• Sidebar apps should expose a /settings route in the app sidebar. Put <LanguagePicker /> in that settings page, usually in a Language or General section, and keep the header language icon only as a quick-access shortcut.
• Settings pages should include an "Agent settings" row/card that calls openAgentSettings() from @agent-native/core/client to open the right agent sidebar's Settings tab. Localize the title, description, and button.
• Use useFormatters() for dates, numbers, relative time, and lists instead of embedding formatted values in translation strings.
• Do not translate stable identifiers: action names, route names, enum values, app-state keys, database values, protocol fields, env var names, or provider names.

Plurals And Placeholders

Plural strings use i18next/CLDR suffixes. Do not force every locale to copy English plural categories:

• English uses _one and _other.
• Chinese and Japanese usually use _other.
• Arabic uses _zero, _one, _two, _few, _many, and _other.

Keep interpolation placeholders identical across locales, such as {{count}}, {{name}}, or ICU-style {count} arguments.

RTL

New UI should be RTL-safe. Prefer logical CSS utilities/properties such as ms-*, me-*, ps-*, pe-*, start-*, end-*, text-start, and text-end when direction matters. Avoid hardcoded left/right positioning for new localized UI unless it is genuinely physical.

Verification

Run:

pnpm guard:i18n-catalogs

For broader changes, also run the affected template tests and pnpm typecheck. Machine translation is only a starting point; high-visibility strings need human review.