i think there is a hack that turns everything back to english
also this port is the only time beavis and butthead was dubbed in japanese, i'm pretty sure the show over in japan only had subtitles

Looking around, there are only two things that I can think of why it only got a Japanese release, it could even be both. One was a rejection from SCEA (Sony Computer Entertainment America) as it featured 2D graphics. They were very picky when it came to 2D and why only a few did get a release. It could still get a release in PAL regions though.

The other thing is the most likely. Viacom New Media and ICOM, both publishers and developers collapsed in 1997 and this would have been one of the casualties of the closure. The Japanese publisher probably got whatever build was completed and did a localisation. If you look at the credits, most of the game was still done in the US and still credits the English cast (why credit them if it's Japanese only) so yeah...

I wonder if there's an English prototype floating about...

Yeah, I am aware of that, but I still wonder why this port was left in Japan

It's only this port, the PC version still had a US release

Okay, how is a Beavis and Butthead game of all things left in Japan? I thought that show never appealed to the Japanese audience

Uh huh huh huh... We're in Japan.