Support session title auto-generation in non-English languages (e.g. Japanese)

Feature Request

Problem

Currently, auto-generated session titles are always in English, regardless of the user's language settings or conversation language. For non-English speaking users (e.g. Japanese), this makes it difficult to quickly identify sessions when browsing session history.

Proposed Solution

Allow session title auto-generation to respect the user's preferred language. This could be achieved by:

1. Adding a sessionTitleLanguage setting in settings.json
2. Or inferring the language from the existing language setting
3. Or detecting the language of the conversation content

Use Case

As a Japanese-speaking user, most of my conversations with Claude Code are in Japanese. When I look at my session list, all titles are in English, which creates a cognitive disconnect. Having Japanese session titles would significantly improve my workflow and session management.

Current Workaround

Using /rename manually each session, but this adds friction and is easy to forget.

Additional Context

The language setting in settings.json already controls Claude's response language, so extending this to session titles would be a natural and consistent improvement.