Feature request: UI language/locale configuration

Feature Request

Is your feature request related to a problem?
The Claude Code CLI interface (permission prompts, "Allow/Deny" options, status messages, spinners, etc.) is hardcoded in English. There is no way to configure the UI language.

Describe the solution you'd like
A locale or language setting in settings.json (both global ~/.claude/settings.json and project-level .claude/settings.json) that changes the language of all UI elements:

• Permission prompts ("Allow once / Allow always / Deny")
• Status messages and spinners
• System messages and confirmations
• Option labels in interactive prompts

Example configuration:

{
  "locale": "es"
}

Describe alternatives you've considered

• Using CLAUDE.md instructions to change response language — this only affects Claude's generated text, not the CLI interface elements.
• The existing language key in settings — unclear if it works and does not affect UI elements regardless.

Additional context
This would make Claude Code more accessible to non-English-speaking developers. Supporting at least major languages (Spanish, French, Portuguese, German, Japanese, Chinese, Korean) would significantly improve the user experience.