[Feedback]: Add multi-language (i18n) support to the desktop app

首先梳理桌面应用的设置和面向用户的 UI 入口，然后确定当前如何处理语言选择和系统语言检测。完成的标准是具备可扩展的本地化层、初步的简体中文支持、Settings 中的语言选择器、本地化的日期和数字，以及有文档说明的翻译贡献流程。

What problem are you trying to solve?

The desktop app currently ships with an English-only UI. Users who are not fluent in English (Simplified Chinese, Turkish, Japanese, Korean, Spanish, etc.) struggle to discover and understand features, which hurts onboarding and daily usage.

There are already several separate requests asking for individual locales - #43 (Turkish), #47, #53 and #74 (Simplified Chinese) - which clearly shows real demand. But each request only covers one language, and the underlying gap is that the app has no i18n/localization framework at all, so users cannot switch the interface language.

What would improve it?

Add a proper internationalization (i18n) layer to the desktop app:

• Externalize all user-facing strings into locale resource files (e.g. JSON) instead of hardcoding English in components.
• • Detect the OS/system language on first launch and add a Language selector in Settings to override it, applied without restart if possible.
• • • Ship an initial set of locales, at minimum Simplified Chinese (zh-CN), plus a documented way for the community to contribute new translations.
• • • • Localize dates, numbers and relative times, not just labels.
• • • • • Keep it extensible so more languages (Turkish, Japanese, Korean, Spanish, ...) can be added later.
          This single change would resolve the multiple one-off localization requests and give all non-English users a first-class experience.

What do you do today?

Today the UI is English-only and there is no language option in Settings. Users either work in English or look for unofficial patches. Related issues: #43, #47, #53, #74.

Product area

Settings