[BUG] Claude Code reverts to English after context compaction

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?

When a conversation reaches the context limit and Claude Code compacts it, the assistant forgets the language in which the conversation was being conducted
and switches back to English, even if the entire conversation was in another language (e.g., Spanish).

What Should Happen?

1. Start a conversation with Claude Code in a non-English language (e.g., Spanish).
2. Continue the conversation until the context is compacted.
3. Observe that Claude Code's next response is in English instead of the original language.

Error Messages/Logs

none

Steps to Reproduce

1. Start a conversation with Claude Code in a non-English language (e.g., Spanish).
2. Continue the conversation until the context is compacted.
3. Observe that Claude Code's next response is in English instead of the original language.

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

v2.1.141 Claude code

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_