[FEATURE] Session titles should be generated in the user's language (re-opening #33546, #35243, #35799)

Problem

Session titles in the sidebar are always auto-generated in English, even when:

• settings.json has "language": "ja" configured
• CLAUDE.md instructs to respond in Japanese
• The entire conversation is conducted in Japanese

This is especially painful for users with many sessions — scanning through English titles to find a Japanese conversation is inefficient.

Previously Reported (all closed without fix)

• #33546 (original, closed as stale)
• #35243 (closed as duplicate)
• #35799 (closed as duplicate)

Re-filing per the auto-close message: "Please open a new issue if this is still relevant."

Expected Behavior

Generate session titles in the language of the conversation, or respect the language setting in settings.json.

Workaround Request

A /rename slash command would also help as an interim solution.

Environment

• Claude Code 2.1.92
• macOS / Windows 11