not necess.
Lots of cam sites have multilanguages interface (livestream I believe has several landing pages in diff. languages) but they depend on studios to provide the actual cam girls or freelancers that join aff programs online, in the later case I don't think all the paperwork is being translated. + you have to factor in that lots of models don't want to do shows for "locals", hence japanese customers may not be able to see japanese performers (depending on the precision of the IP "filters" in place)
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just to be clear, what I meant to say is that:
even if there was a few japanese performers in the network, chances are that
A) they would know basic english
B) they would have the ability to filter out japanese clients
so until one of the big cam sites partner with a japanese studio, I don't think you're gonna find any meaningful "japanese content" on there