I don't usually play translated video games..
Playing games in english as a teenager has taught me a lot of english.
I've just tried the hungarian translation for Mount&Blade Warband, it's not too bad, although it exhibits some of the usual partially translated
issues. (Some of that might be because of a mod I have installed though..)This guy
wants to say "Let's raise our winecups in honor of our host, Sanjar khan", but he fumbles something like "let's raise our glasses full of winecup drink". This is probably a difficult game to translate, because a lot of these sentences are stiched together from parts, as they have dynamic elements (the type of drink and the name of the host changes based on the situation).
Other than that, there are only a few errors here and there, and some things sound a bit awkward, but only a bit. The overall the experience is a bit jarring because of the partial translations, so I prefer english..
I've also tried Portal 2, it's alright, but the accented characters look weird: http://imgur.com/a/72saj
Much of game-jargon is hard to translate, the way they translated "single player game" for portal 2 sounds weird because the word for "player" is derived from the word for "game"...
But to answer your question, nope, I don't know of any fantastically bad translations. Hell, the Warband one might've actually been really good, with a bit more attention.