[FEATURE] Feature request: Make sidebar conversation title language match user's input language

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

Problem

The auto-generated titles in the sidebar are often in English even when the
entire conversation is conducted in Japanese. This makes it harder to scan
and identify past sessions for non-English users.

Example

• My conversations are 95%+ in Japanese
• First user message is pure Japanese (e.g., "前セッションからの引き継ぎ...")
• Yet some titles come out in English (likely because the content contains

technical terms like filenames, "Phase 6", etc.)

• Inconsistency: some sessions get Japanese titles, others get English titles

for similar content

Proposed Solution

Proposed solution

Either of:

1. A setting in ~/.claude/settings.json to specify preferred title language

(e.g., "titleLanguage": "ja" or "auto")

1. Default behavior: match the dominant language of the conversation
2. Allow manual rename of session titles from the sidebar

Environment

• Claude Code version: 2.1.114
• Platform: macOS (VSCode extension / native app)
• Language: Japanese

Additional context

Even when explicitly starting a new session with Japanese text, the title
often renders in English, suggesting the summarizer model's system prompt
biases toward English output regardless of input language.

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_