Motivation

• Introduce a simple internationalization layer so the UI can present localized labels and copy and allow users to pick a language.
• Provide an initial Chinese (zh-CN) translation set for core navigation and UI strings.
• Persist language preference in settings so the selected language is applied across sessions.

Description

• Add a new i18n.ts module exposing tr, UiLanguage type, resolveUiLanguage, and setUiLanguage, and include a zh-CN translation dictionary.
• Wire language preference into persistent settings by adding language to UiSettings and persisting it in storage.ts.
• Add a language selector to the topbar and replace many hard-coded UI strings with tr(...) calls across app-render.ts, app-render.helpers.ts, navigation.ts, and other view files.
• Ensure the selected language is applied by calling setUiLanguage and updating document.documentElement.lang when settings are applied and when the app connects.

Testing

• Built the TypeScript project with the project build (tsc / npm run build) and the build completed successfully.
• Ran the project's automated test suite (npm test) and the tests passed.

Codex Task