What it listens for, and what it answers in

Transcription listens in one language at a time. Left alone it follows this Mac’s own language, and the picker names which one — a call in another language needs one pick, in Settings › General or from the globe beside the transcript.

The answer language is a toggle of its own, so you can be transcribed in one language and handed a line to say in another. Getting these two wrong together has a very specific result — a call where every suggestion arrives in a language you cannot say out loud.