The Stuttgart fans adopted it in 2003 after Celtic played them in the UEFA Cup. Don't know why the rest have, but they're pretty good at it.
I just heard it was Dortmund fans after Liverpool Vs Alaves in 2001.
Apparently for an hour after the whistle Liverpool fans stood there singing and it even made the Dortmund press the next day (according to someone who was there). Ever since, Dortmund fans adopted it and it's been doing the rounds around Germany ever since.
I would guess it was a combination of the two. Makes more sense as to why it is all over Germany rather than just in Dortmund. Apparently Dortmund still sing it during European nights.
Might have been, similar reason. I was in Stuttgart & it was one of the friendliest Euro trips I've been on, about 20,000 of us went over. We all got tickets, obviously not all in the Celtic end.
I know that the Stuttgart fans were quite surprised that the Rangers fans didn't appreciate it when they played there the year after
