Model responded in Korean instead of following conversation language

Description

During a conversation conducted entirely in Chinese, Claude Code unexpectedly switched to Korean in one response.

Steps to Reproduce

1. Start a conversation with Claude Code in Chinese
2. Ask a technical question in Chinese
3. Observe that one of the responses was returned in Korean instead of Chinese

Expected Behavior

Claude Code should respond in the same language as the user's messages (Chinese in this case).

Actual Behavior

One response was returned in Korean (한국어) despite the entire conversation being in Chinese.

Additional Context

This appears to be an inconsistency in language detection/following behavior. The model should consistently respond in the language used by the user.