[FEATURE] Feature Request: Support i18n / Chinese locale for built-in commands output (e.g. /cost)

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

内置命令（如 /cost、/help 等）是系统预定义的，我无法修改它们的描述语言。

Proposed Solution

希望内置命令（如 /cost、/help 等）的输出支持中文或多语言切换。
目前所有内置命令的描述和输出都是英文，对中文用户不够友好。

建议：

• 支持通过配置切换语言（如 locale: zh-CN）
• 或至少支持命令输出的国际化

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_