Do we have a tag for japanese text on images? Someone got rid of japanese_commentary but I don't think that's the right one either.
We don't. It is expected that most text on posts will be in Japanese, so we only tag the other languages. If a user wants to filter out non-Japanese languages, they can search for translated -*_text or translation_request -*_text, though some users forget to add translation_request to these posts.
The commentary/commentary_request tags are for text in the "Artist's commentary" box below the image, not on the actual image.