[Bug] German umlauts randomly replaced with ASCII substitutes in responses

Bug Description
German umlauts (ä, ö, ü, ß) are randomly replaced with ASCII substitutes (ae, oe, ue, ss) in responses. This is a regression that started ~2-3 months ago and is getting worse over time. Many users are affected, see https://github.com/anthropics/claude-code/issues/14131. The bug is reproducible and well-documented. Please prioritize a fix.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.50
• Feedback ID: f5364169-21c5-4549-a9c1-61a70fcf1ba6

Errors

[{"error":"Error\n    at <anonymous> (/$bunfs/root/claude:79:11055)\n    at <anonymous> (/$bunfs/root/claude:93:10263)\n    at emitError (node:events:43:23)\n    at <anonymous> (/$bunfs/root/claude:92:3470)\n    at emitError (node:events:43:23)\n    at <anonymous> (node:_http_client:253:22)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:95:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-02-24T17:22:37.594Z"},{"error":"Error\n    at <anonymous> (/$bunfs/root/claude:79:11055)\n    at <anonymous> (/$bunfs/root/claude:93:10263)\n    at emitError (node:events:43:23)\n    at <anonymous> (/$bunfs/root/claude:92:3470)\n    at emitError (node:events:43:23)\n    at <anonymous> (node:_http_client:253:22)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:95:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-02-24T17:22:37.637Z"},{"error":"Error\n    at <anonymous> (/$bunfs/root/claude:79:11055)\n    at <anonymous> (/$bunfs/root/claude:93:10263)\n    at emitError (node:events:43:23)\n    at <anonymous> (/$bunfs/root/claude:92:3470)\n    at emitError (node:events:43:23)\n    at <anonymous> (node:_http_client:253:22)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:95:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-02-24T17:22:38.465Z"},{"error":"Error\n    at zj (/$bunfs/root/claude:92:1144)\n    at <anonymous> (/$bunfs/root/claude:93:10097)\n    at emit (node:events:92:22)\n    at endReadableNT (internal:streams/readable:861:50)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:95:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-02-24T17:22:39.316Z"},{"error":"Error\n    at <anonymous> (/$bunfs/root/claude:79:11055)\n    at <anonymous> (/$bunfs/root/claude:93:10263)\n    at emitError (node:events:43:23)\n    at <anonymous> (/$bunfs/root/claude:92:3470)\n    at emitError (node:events:43:23)\n    at <anonymous> (node:_http_client:253:22)\n    at processTicksAndRejections (native:7:39)\n    at request (/$bunfs/root/claude:95:2149)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-02-24T17:22:39.418Z"},{"error":"AbortError: The operation was aborted.\n    at unknown\n    at abortChildProcess (node:child_process:935:42)\n    at onAbortListener2 (node:child_process:35:24)\n    at abort (unknown)\n    at <anonymous> (/$bunfs/root/claude:2511:1362)","timestamp":"2026-02-24T17:22:48.727Z"}]