I have also been testing on beta releases and on public release as well but not working for Arabic locale.
Error Domain=SFSpeechErrorDomain Code=1 "transcription.ar asset not found after attempted download." UserInfo={NSLocalizedDescription=transcription.ar asset not found after attempted download.}
I have also reported this on Radar https://feedbackassistant.apple.com/feedback/20276792
Topic:
Media Technologies
SubTopic:
Audio
Tags: