[FEATURE] Allow configuring language for auto-generated session names

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

Auto-generated session names are always in English, regardless of the user's language preferences or conversation language. For non-English users (e.g., Japanese), this creates a disconnect — the entire conversation is in their native language, but the session name appears in English, making it harder to identify and navigate between sessions.

Currently there is no setting to control the language of auto-generated session names. The naming is handled by the harness, so CLAUDE.md instructions have no effect on it.

Proposed Solution

Add a configuration option to control the language of auto-generated session names. This could be:

1. A setting in settings.json: "sessionNameLanguage": "ja"
2. Or auto-detect the language from the user's CLAUDE.md language preference or OS locale
3. Or match the language of the conversation content

This would help non-English users navigate their session history more naturally.

Alternative Solutions

Currently the only workaround is manually renaming sessions via /sessions, which is tedious for every session. Adding instructions in CLAUDE.md has no effect since session naming is handled by the harness, not the model.

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

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Additional Context

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