claude-code - 💡(How to fix) Fix Language instruction ignored: Claude responds in Japanese despite explicit Traditional Chinese requirement in CLAUDE.md [1 comments, 2 participants]

Summary

Claude Code repeatedly responds in Japanese or Korean despite an explicit instruction in CLAUDE.md to always use Traditional Chinese (台灣正體中文) and never use Japanese, Korean, or Simplified Chinese.

Environment

• Claude Code version: unknown (VSCode extension)
• Model: claude-sonnet-4-6
• Platform: macOS (darwin 24.6.0)

CLAUDE.md instruction

## 語言設定

永遠使用台灣正體中文回覆，不得使用日文、韓文或簡體中文。

What happened

This has occurred across multiple sessions. Claude switches to Japanese or Korean mid-conversation during technical work, despite the CLAUDE.md instruction being loaded and visible in context.

Example 1 (screenshot provided)

After a git push operation, Claude responded entirely in Japanese — then caught itself, apologized in Japanese, and continued to respond in Japanese while attempting to correct the issue:

commit と push 完了。lint-staged の index.lock エラーは先ほどの background プロセスの残骸で、最終的には成功している。

申し訳ありません、日本語になっていました。再度、正體中文で： storefront に push 完了しました。...

The "correction" was itself still in Japanese.

Example 2 (this session)

After a gh pr view tool call returning English-only JSON, Claude responded in Japanese:

Backend tests が FAILURE のままです。CI が通っていない状態では merge できません。

ただ、このPR（chore/codex-pr-review-agents）の内容は AGENTS.md への変更で...

Example 3 (reported, no screenshot)

The user has also received Korean responses on separate occasions.

What should have happened

All responses should be in Traditional Chinese regardless of the operation being performed.

Key observations

• The project codebase contains only Traditional Chinese and English — no Japanese or Korean anywhere in the repo
• All team members write in Traditional Chinese; other team members do NOT experience this issue with their own Claude Code sessions
• The violation occurs after tool calls (git, gh) that return English-only output — there is no Japanese or Korean content in the conversation context that could explain the language switch
• After being corrected, Claude sometimes apologizes and "switches back" — but the apology itself is still in Japanese
• The issue recurs across sessions despite being recorded in both CLAUDE.md and the auto-memory system
• The pattern is specific to this one user, suggesting something in their session context or environment triggers it — but what that is remains unknown