This is just from personal experience and should in no way be seen as the general rule: For me the game (seemingly) worked without a hitch (german voices, english subtitles). But then again, maybe I missed certain things that I didn't even know were there because of the language hack.
I did have one bug though, the final ending movie wouldn't play for me, but I'm not sure if that's language hack related, or just an issue I happen to have.
