Feature Request: Support configurable display language for error messages (i18n/localization)

Summary

Currently, error messages displayed in Claude Code are only available in English. There is no way to configure the display language, making it difficult for non-English speakers to understand error details quickly.

Motivation

When Claude Code encounters errors from applications or tools, the error messages and codes are always shown in English. For users whose primary language is not English (e.g., Japanese), this creates friction — especially during debugging — as users must mentally translate error messages on top of understanding the technical content.

Proposed Solution

Add a configurable language/locale setting (e.g., in settings.json) that allows users to select their preferred language for error messages and UI text displayed within Claude Code.

Example configuration:

\\\json
{
"locale": "ja"
}
\\\

This would allow Claude Code to display error messages, warnings, and other output in the configured language when translations are available, falling back to English when not.

Expected Behavior

• Users can set a preferred locale/language in Claude Code settings
• Error messages and UI text are displayed in the configured language
• Graceful fallback to English if a translation is not available for a given message

Current Behavior

All error messages and UI text in Claude Code are displayed in English only, with no configuration option to change the display language.

Additional Context

• This is a common feature in developer tools (e.g., VS Code supports locale configuration)
• Supporting i18n would make Claude Code more accessible to a global audience
• Initial support could start with major languages such as Japanese, Chinese, Spanish, French, etc.

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Submitted by a Japanese-speaking user who would like to see error messages displayed in Japanese.