0003. Bilingual UI (zh-CN / en)

• Status: Accepted
• Date: 2026-10-09
• Deciders: tseka

Context

All UI strings and aria-labels are hardcoded Chinese. No i18n library.

Decision

• Support zh-CN and en across the landing page and the app.
• Library: vue-i18n (composition API, typed message schema).
• Default locale en. Resolution: explicit user choice (persisted) → navigator.languages best match → en. Public pages use path locales (/home en as x-default, /zh/home).
• <html lang> follows the active locale.
• Message keys are namespaced by feature. Brand name (ADR 0001) is not translated.
• /home locale variants are crawlable (hreflang).

Consequences

• Every new user-visible string goes through t(); enforced by lint on .vue templates.
• Migration is incremental per feature; Chinese is the source locale during migration.