[BUG] Randomly adds word from a different language. Using English with One word in Russian

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?

I've seen similar bugs to this posted, but the languages seem to be far more similar. In this instance, interweaving a Russian word for English, it seems more misaligned with the expectation.

i was talking to claude opus 5 and it wrote me "...My честный recommendation on order:..."

I asked claude about it

❯ why did you write: честный to me?

⏺ That was an error on my part — a stray token. It should have read "my honest recommendation." No hidden meaning;
  nothing about the content changes.

Nowhere in its context was anything related to Russian. I presume it is due to the fact that:

че́стный
The Russian word честный (pronounced chest-nyy) translates to honest, fair, or truthful in English. It describes a person who tells the truth, does not cheat, or an action that is done fairly and legally.

What Should Happen?

full response in english

Error Messages/Logs

Steps to Reproduce

I was not able to reproduce. I tried asking it: can you spend some time talking about the different elements of how to be: honest, fair, or truthful

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

claude 2.1.220.603

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_