Feature request: Multi-language UI with a language selector (i18n)

Feature Description

Problem

The entire product surface — website, docs, desktop app, and CLI — is English-only.
There is no language option anywhere in Settings (General / Appearance / Agent /
Taste / MCP / Account), and no way for users to switch the interface language.

For a tool positioned as a frontier coding agent, this is an adoption bottleneck
in non-English markets.

Suggested solution

Add a Language dropdown under Settings → General, letting each user
freely pick their interface language. Suggested launch set:

• English (default)
• 简体中文 (zh-CN)
• 日本語 (ja)
• Español (es)
• Português (pt-BR)
• Deutsch (de) / Français (fr) / 한국어 (ko) as follow-ups

Scope for v1: desktop app UI + the most-visited docs pages.

Implementation notes:

• Build the i18n layer on a standard framework so adding a language is a
  translation file, not a code change
• If in-house translation isn't planned, a community workflow (e.g., Crowdin)
  keeps marginal cost near zero — especially if the i18n layer is added early
  rather than retrofitted later

I'm filing this as a product suggestion; happy to help test new languages once
shipped.

Use Case

• Market size: The majority of the world's ~30M developers are non-native
  English speakers. China alone has ~7M professional developers (the largest
  single population globally), and strong dev communities exist across Japan,
  Brazil, Korea, and Spanish-speaking Latin America.

• Competitive parity: Cursor, Windsurf, and Trae already ship official
  multi-language / Simplified Chinese UIs. Trae's rapid growth is partly
  attributed to localization. English-only is becoming a visible gap.

• Brand consistency: Non-English content about Command Code today is almost
  entirely third-party reviews and machine-translated blog posts — mixed
  messaging, no quality control, no positioning leverage. Official localization
  would consolidate all of it.

• Low cost, compounding return: A language dropdown is a one-time i18n
  investment; each new language after that is just a translation file, often
  community-contributed.

Additional Context

No response

How important is this to you?

Important for my workflow

Bắt đầu bằng cách lập bản đồ điểm vào Settings → General của ứng dụng desktop và các trang tài liệu được truy cập nhiều nhất được nêu trong issue. Xác định cách biểu diễn tùy chọn ngôn ngữ và bản dịch, sau đó định nghĩa các ngôn ngữ được hỗ trợ khi ra mắt và hành vi fallback. Công việc được xem là hoàn tất khi một ngôn ngữ giao diện có thể chọn hoạt động cho UI desktop v1 và các trang tài liệu trong phạm vi.