Feature Request: i18n / Localization support for UI strings (permission prompts, etc.)

Summary

Currently, all UI strings in Claude Code (permission prompts, menu options, status messages) are hardcoded in English. For non-English speaking users, this creates friction — especially the permission dialogs that appear frequently during sessions.

Proposal

Add internationalization (i18n) support so that UI strings can be displayed in the user's preferred language.

Example: Permission prompt (current → Japanese)

• "Do you want to proceed?" → 「続行しますか？」
• "Yes" → 「はい」
• "No" → 「いいえ」
• "Esc to cancel · Tab to amend" → 「Escでキャンセル · Tabで修正」

Motivation

• Claude Code is used globally; many users are non-English speakers
• Permission prompts appear very frequently, making localization high-impact
• A locale setting (e.g., LANG env var or config option) would be a lightweight way to start

Possible Approach

1. Extract hardcoded UI strings into locale files (e.g., en.json, ja.json)
2. Detect locale from system environment or add a config option
3. Start with high-frequency strings (permission prompts) as a first pass