what languages should you promote your band in?

Just use English, Spanish and German, if you want to have 3 languages. If you are really looking for 4 I'd add French. The rest of the languages are minorities. If I had a site I would have it in all the languages I can speak, though, but that's just because I like languages.
 
Otherwise I think that people in "our genre" dig deeper, anyway.
So, if theyre interested in your music and your promo text is in english, it should'nt make a difference.
 
In case it is Epic Power Metal, you can also add Elfic.

ok, i'm convinced... its english and elven. everyone else can kiss my ass! now i just have to contact my old friend who's a 7th class druid lord and can translate my newsletters into runes. keep an eye out for me, i'll be taking over the world soon. at least in his D&D kingdom!

but seriously... japanese is a great idea that i totally forgot about. of course, its not one of the romantic languages that i actually had contacts to translate for. dammit! but i agree with you, the japanese market is very lucrative, something i need to reconsider. but its nice to know that i wont have to spend time/energy/money getting things translated into multiple languages for now.