Replies drift into English

“Each time I corrected it ("한국말", "korean plz", …), it apologized, rewrote the same content in Korean, then drifted back to English a few turns later.”

Is this your bug? What gets counted gets fixed. Pile on.

Paste this into your agent. It files your report, with your error and version.

I hit this bug: rapsheet.dev/sheets/claude-code/issues/501/file
Follow it to file my report. Show me the text before you send.

No install. No account. Public and anonymous. The link asks your agent for one report, nothing else. What it sends

Still happening. 6 reports and thumbs-up in each of the last two weeks, down from 18 a week at the late-September peak. A workaround is known.

Replies drift into English despite configured non-English language. Progress notes between tool calls and final reports switch to English in long sessions; corrections hold only a few turns.

Is this your bug?

File my report

Where: Model responses
Versions: 2.1.278 to 2.1.317
Platforms: Linux, macOS, Windows
How bad: Breaks a normal workflow.

Not quite your bug?

Response language switches mid-session3 people

Original reports19, newest first

Nov 5, 2026Opus 5.5 answers in English from the first reply despite a Korean CLAUDE.md instruction (not a long-session effect)#107449
Nov 3, 2026Claude responds in English instead of user's Korean input#106967
Nov 3, 2026Assistant drifts from configured output language (German) to English after English tool output#106911
Nov 3, 2026Progress notes and visible thinking drift to English in a Hebrew session despite CLAUDE.md (Desktop Code tab, Windows)#106893
Oct 28, 2026Claude responds in English mid-session despite Japanese language setting#105644
Oct 21, 2026Model repeatedly switches to English mid-session for a Spanish-speaking user (status lines between tool calls), despite explicit language instructions#104137
Oct 21, 2026Switches to English mid-session despite Korean-only CLAUDE.md, memory and repeated corrections (macOS CLI)#104035
Oct 20, 2026Intermediate progress updates ignore CLAUDE.md language setting during subagent-driven-development#103672
Oct 13, 2026Claude switches to English mid-session despite Japanese conversation and "language": "japanese" (Windows desktop app)#101940
Oct 5, 2026Responses drift into English mid-task despite language: "japanese" and CLAUDE.md language rules#99800

Show the newest 18 of 19Show only the newest 10

Oct 5, 2026CLI ignores non-English language requests in output#99704
Oct 5, 2026Opus 5.5 / Sonnet 5.5 drift into English mid-session despite German user input#99603
Oct 4, 2026Language setting reverts to English despite Korean configuration#99494
Oct 1, 2026Claude ignores language preference and responds in English despite Spanish instructions#98848
Oct 1, 2026Repeatedly switches to English despite CLAUDE.md + memory + repeated in-chat instructions to reply only in Japanese#98633
Sep 29, 2026지정한 응답 언어(한국어)를 도구 호출 사이 중간 안내에서 반복적으로 지키지 않음#98145
Sep 24, 2026Opus 5.5 ignores output-style language rule after tool chains (0.4% -> 4.2% English)#96601
Sep 23, 2026Replies drift into English right after reading English tool output, despite a CLAUDE.md rule requiring Japanese; corrections do not hold#96326