feat: publish HoloLake model-native living system source

product-source/hololake-platform/docs/adr/0084-app-localization-foundation.md

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+---
+type: ADR
+id: "0084"
+title: "App-owned localization foundation"
+status: active
+date: 2026-04-26
+---
+
+## Context
+
+Tolaria was effectively English-only. Users requested a general i18n foundation and Chinese-language support. We need a path that lets the UI adopt additional locales without pushing UI-language preferences into vault files or making every partially translated string a runtime failure.
+
+## Decision
+
+Tolaria owns a dependency-free frontend localization layer in `src/lib/i18n.ts`.
+
+- English is the canonical fallback locale.
+- Simplified Chinese (`zh-Hans`) is the first additional locale.
+- `ui_language` is an installation-local app setting in `~/.config/com.tolaria.app/settings.json`; `null` means "follow system language when supported, otherwise English".
+- Missing translation keys fall back to English.
+- App-level chrome receives locale through props from `App.tsx`, following the existing props-down/callbacks-up architecture instead of introducing global React context.
+- Language switching is exposed in Settings and through command-palette actions.
+
+## Alternatives considered
+
+- **Add an i18n dependency now**: useful long term, but unnecessary for the first locale and would add framework surface before we know Tolaria's locale workflow.
+- **Store language in the vault**: rejected because UI language is an installation preference, not content structure.
+- **Translate ad hoc strings inline**: rejected because it would make fallback behavior inconsistent and future locales expensive.
+
+## Consequences
+
+- New UI strings should be added to `src/lib/i18n.ts` first and rendered through `translate()` / `createTranslator()` where the surface already receives locale.
+- Partially translated locales remain usable because English is the fallback for missing keys.
+- Locale choice changes UI chrome immediately after settings save or command-palette language commands without reopening the vault.
+- Larger feature surfaces can migrate to the shared localization module incrementally.