They translated what was basically important (Hud, text from enemies, omake pictures) but still pet background stuff like the kappa sign untranslated. The returning characters used the same voice actors from the Sega CD game, so there's some consistency there if you played that. Though unlike the Sega CD game, they dubbed the in-game speech too this time around. Don't remember cringing at the dub so its pretty decent for what it was. Im sure there is creative liberties done, but for a silly game like this, I don't think being 100% faithful is possible.
Btw, what was the letter from the creators? I might be forgetting something...