Feature Request: Localization/i18n support for UI messages

Feature Request: Localization support for UI messages

Currently, all Claude Code UI messages (welcome message, status messages, error messages, prompts, etc.) are displayed in English only, with no way to configure the display language.

Requested Feature

Please add internationalization (i18n) support so that UI messages can be displayed in languages other than English, such as Japanese.

Use Case

Users who primarily work in Japanese (or other non-English languages) can configure Claude's response language via CLAUDE.md, but the CLI's own UI messages remain in English, creating an inconsistent experience.

Proposed Solution

• Add a language setting in settings.json or support a CLAUDE_LANG environment variable
• Provide localized message bundles for major languages (Japanese, French, Spanish, etc.)

This would greatly improve the experience for non-English speaking users.