Hi, Irishbrat. I always thought the traditional German birthday song was "Hoch soll er leben," but this page (click) says the American "Happy Birthday" song (sung in English) is more common. Here's what they say:

German Happy Birthday Song (traditional)    Hoch soll er leben!/Hoch soll sie leben! Hoch soll sie leben! (Long may she live!) Hoch soll sie leben! Dreimal hoch! (Three cheers!) Note: This brief song also serves as the German equivalent of “For He's a Jolly Good Fellow.” The tune is different from that of “Happy Birthday” in English, which is actually heard more often at German birthday parties than “Hoch soll er leben!”

MIDI can be found here (click)
If I were in your shoes, I'd sing "Hoch soll er/sie laben leben" ("er" is masculine, "sie" feminine).
-Joe Offer (e-mail sent)-