[BUG] Claude randomly switches to Korean when responding in a Chinese conversation

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Description:
During a conversation conducted entirely in Chinese, Claude occasionally switches to Korean mid-response without any prompt or reason. This happens seemingly at random, typically after tool calls or context switches.

Steps to reproduce:

Start a conversation in Chinese
Make several tool calls (e.g., file edits, bash commands)
Observe that some responses are partially or fully in Korean
Expected behavior:
Claude should maintain the language of the conversation consistently throughout the session.

Actual behavior:
Claude randomly responds in Korean instead of Chinese.

Environment:

Claude Code VSCode Extension
Model: claude-sonnet-4-6

What Should Happen?

random

Error Messages/Logs

Steps to Reproduce

Just talk with Claude in Chinese, it sometimes return Korean.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.181 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_