Add support for localized/translated UI messages (e.g. permission prompts)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Currently all system UI text in Claude Code — including permission-request dialogs ("Do you want to allow X to run Y?") — is hardcoded in English, with no locale/language setting available (no LANG env var support, no settings.json key, no CLI flag).

Other coding CLI tools (e.g. OpenAI Codex) already support localized UI output based on system locale. It would be very helpful for non-English-speaking users if Claude Code offered the same, at least for the most common prompts (permission requests, error messages).

Proposed Solution

Suggestion: Respect the OS locale (or a CLAUDE_CODE_LANG/settings.json language key) to translate built-in UI strings.

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_