Russian language (i18n) support for Claude Code UI

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

Claude Code interface (menus, prompts, system messages, errors) is English-only.
Russian-speaking developers must use an English UI even though Claude itself
responds perfectly in Russian. This creates friction for a large developer
community across Russia and CIS countries.

Proposed Solution

Add i18n/localization support to Claude Code CLI. Ideal UX:

• Set language via config: claude config set language ru
• Or via environment variable: CLAUDE_LANG=ru
• All UI text (menus, prompts, errors, slash command descriptions)

rendered in the selected language.

Alternative Solutions

Currently there are no workarounds — the UI is hardcoded in English.
Other tools (VS Code, JetBrains IDEs, GitHub Desktop) solve this via
system locale detection or explicit language settings.

Priority

High - Significant impact on productivity

Feature Category

Configuration and settings

Use Case Example

Use Case Example:

1. Russian-speaking developer opens Claude Code in terminal
2. All menus, hints and error messages appear in English
3. Developer must mentally translate every prompt while working
4. With language support: set CLAUDE_LANG=ru once,

all UI appears in Russian automatically

1. Saves cognitive load, especially for non-fluent English speakers

Additional Context

Russian is spoken by ~150M people. Large developer communities exist
in Russia, Ukraine, Belarus, Kazakhstan. VS Code already supports
Russian via language packs — Claude Code could follow the same pattern.