Japanese transcription can't be create by Video Indexer.
For example, using same video file and tried Japanese and English Transcription mode. (The language of the video is Japanese)
Result, English transcription could create , but Japanese could not create.
I tried region == WUS2,JapanEast
. Both results were the same.
There is currently a live site in Speech services preventing Japanese transcription. We are rolling out a fix and it should get resolved. We will update you here.