Feature Request: Add Chinese (Simplified) localization / i18n support

Description

Claude Code currently only has an English UI. For Chinese users, having to mentally translate error messages and help text every time is tiring.

Would love to have a Chinese interface.

What needs translating

• CLI prompts and menus
• Error and warning messages
• --help output
• Progress and status messages

Implementation suggestion

Add a language config option in ~/.claude/settings.json, or read the system's LANG environment variable. A standard library like i18next or gettext would work.

A --lang zh-CN CLI flag for temporary switching would also be nice.

Example

Current:

$ claude --help
Usage: claude [options] [command]

Expected:

$ claude --help
用法: claude [选项] [命令]