This topic came to me when trying to impart the wisdom of Rammstein on my friend. I love Rammstein (for anyone who doesn't know, they're a german band) even though I don't know german. I told him that I love them, but he said he can't stand them because he can't understand the lyrics. I however, have listened to them for some time, and actually consider the english language a handicap for metal groups, that german just sounds better.
So what do you think about languages that aren't your own in music?