[Bug] Claude Opus occasionally uses moskovian(russian) orthography instead of Ukrainian in system-prompted responses

Bug Description
▎ Claude (Opus 4.7) when instructed to "respond in Ukrainian" via system prompt occasionally uses moskovian (russian) letters (e.g., "и" instead of "і") or russified word forms in Ukrainian responses.
▎ This is unacceptable for paying users. The model must use pure Ukrainian orthography (і, є, ї, ґ) consistently and avoid russisms entirely.

Environment Info

• Platform: linux
• Terminal: guake
• Version: 2.1.150
• Feedback ID: c829022a-34c4-4e90-8598-2e906ff14af2

Errors

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