hermes - 💡(How to fix) Fix [Feature] Add i18n / Chinese language support for the Desktop app

Summary

The Electron Desktop app (apps/desktop/) currently has all UI strings hardcoded in English. The Python backend and CLI already have a mature i18n system (agent/i18n.py + locales/*.yaml) with 16 languages including Simplified and Traditional Chinese — but the Desktop app does not benefit from any of this.

It would be great to add internationalization support to the Desktop app so non-English speakers can use it in their native language.

Current state

What already works

• agent/i18n.py provides a lightweight YAML-based catalog system with dot-path keys
• locales/zh.yaml (355 lines) covers approval prompts, slash command replies, gateway notifications
• locales/zh-hant.yaml covers Traditional Chinese
• Language resolution: HERMES_LANGUAGE env > display.language in config > default English
• Natural aliases like chinese, zh-CN, zh-TW are handled automatically

Proposed approach

Phase 1: Foundation

• Add an i18n library to the Desktop app (e.g. i18next + react-i18next, or @lingui/core)
• Create a locales/ directory under apps/desktop/ with English as the base catalog
• Extract hardcoded UI strings from .tsx files into catalog keys

Phase 2: Chinese translation

• Add zh.yaml (Simplified Chinese) catalog for the Desktop app
• Optionally add zh-hant.yaml (Traditional Chinese)

Phase 3: Language selection

• Add a language picker in Desktop settings (or auto-detect from system locale via app.getLocale())
• Wire display.language from config.yaml so CLI and Desktop share the same preference

Strings to translate (examples)

Key areas with hardcoded English in the Desktop app:

• Onboarding overlay (desktop-onboarding-overlay.tsx): "Sign in", "Paste API key", "Replace current value", placeholder texts
• Boot failure overlay (boot-failure-overlay.tsx): Error messages, reauth prompts
• Chat composer: placeholder text, send button, slash command hints
• Settings/preferences: All labels and descriptions
• Theme names (themes/context.tsx): "Light", "Dark" suffixes
• File tree / preview: Directory labels, "no preview" messages
• Error toasts and notifications

Context

The Electron Desktop app is a separate chat surface from both the classic CLI and the TUI. It uses @assistant-ui/react + nanostores and talks to tui_gateway over JSON-RPC. It does NOT embed hermes --tui — it has its own composer, transcript, and slash-command pipeline.

Since the Desktop app has its own UI layer, it needs its own i18n infrastructure rather than directly reusing the Python backend's catalog (though the translation content could be shared or kept in sync).