Feature Request: Internationalization (i18n) of CLI UI messages

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

All status and progress messages in the Claude Code CLI are hardcoded in English. There is no way to configure the display language for the interface, even when the user interacts with the model entirely in another language.

Examples of affected messages:

• Searching for N patterns, reading N files…
• Musing… (1m 31s · ↓ 661 tokens · almost done thinking with medium effort)
• Reading, Writing, Running, Compiling, etc.

The model already responds in the user's language — but the UI strings remain in English regardless.

Proposed Solution

Users should be able to configure the CLI display language, or at minimum the interface should respect the system locale.

Suggested approaches:

1. Extract all UI strings into locale files (e.g. en.json, pt.json) and resolve at runtime based on a CLAUDE_LANG env var or a settings.json field like "locale": "pt-BR".

1. As a simpler first step, expose a config option to set the display language, even if only a few languages are supported initially.

Alternative Solutions

No viable workaround currently exists. Users working in non-English languages must tolerate the mismatch between their language of choice and the English UI strings displayed by the CLI.

Priority

High - Significant impact on productivity

Feature Category

Interactive mode (TUI)

Use Case Example

1. A developer in Brazil opens Claude Code and starts a conversation entirely in Portuguese.
2. Claude responds fluently in Portuguese throughout the session.
3. However, all status messages—such as Musing…, Reading, Writing, Searching for N patterns—remain hardcoded in English.
4. The jarring contrast between a Portuguese conversation and English UI strings makes the tool feel less polished and accessible to non-English speakers.
5. With this feature, the developer could set CLAUDE_LANG=pt-BR or "locale": "pt-BR" in settings.json, and all UI strings would display in Portuguese.

Additional Context

Platform: Windows / win32-x64
Version: 2.1.186

This affects users who work entirely in non-English languages. The contrast between a Portuguese conversation and English UI strings is jarring, and makes the tool feel less accessible to non-English speakers — a significant portion of the developer community.