## Summary
- Set up i18n infrastructure using i18next with locale files for English
(chat, common, errors, home, settings namespaces)
- Add LanguageSelector component to the settings page for users to
switch languages
- Add language preference field to the app schema and integrate i18next
provider in the app layout and renderer

## Test plan
- Verify the app builds and starts without errors
- Navigate to Settings and confirm the Language Selector is visible and
functional
- Confirm English translations load correctly across all namespaces

🤖 Generated with [Claude Code](https://claude.com/claude-code)
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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Broad UI text refactor plus new runtime language switching could
surface missing keys, incorrect namespaces, or layout regressions,
though changes are largely non-functional and localized to presentation.
> 
> **Overview**
> Adds app-wide internationalization via `i18next`/`react-i18next`,
including a new `src/i18n` initialization with bundled namespaces and
locale resources.
> 
> Introduces a persisted `language` setting (validated by
`LanguageSchema`) plus a new `LanguageSelector` UI, and syncs the active
i18n language at startup in `RootLayout`.
> 
> Migrates many user-facing strings across chat, settings, integrations,
dialogs, banners, and preview panel components to use `t()` translation
keys (with interpolation/plurals) instead of hardcoded English, and adds
an i18n design doc. Dependencies are updated in `package.json`/lockfile.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
a996131500b0f99ea766036084972f9863aca81d. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Add app-wide internationalization with i18next and a language selector
in Settings. The chosen language persists and updates the UI instantly;
ships with English, Simplified Chinese (zh-CN), and Brazilian Portuguese
(pt-BR), aligned with the Linear issue, and migrates UI text across the
app.

- **New Features**
- Initialize i18next/react-i18next with namespaces (common, settings,
chat, home, errors) before render; sync to UserSettings.language on
startup.
- Add LanguageSelector in Settings → General showing only completed
locales; saves validated values and switches UI language.
- Include complete en, zh-CN, pt-BR translations, Intl-based
date/number/relative-time helpers, and docs/i18n.md.

- **Refactors**
  - Replace hardcoded strings with t() across 50+ components.
- Validate settings.language via LanguageSchema.safeParse; defer
changeLanguage to layout sync to avoid duplicates; add error handling
for updateSettings; extract constants in formatRelativeTime.

<sup>Written for commit b670b0489415ca966db1f70f0a1ad3111a455538.
Summary will update on new commits.</sup>

<!-- End of auto-generated description by cubic. -->

---------
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>