I would be willing to translate song lyrics and other material into English (and Swedish if anyone would be interested). I can manage amateur translations from Swedish, Norwegian, Danish and German into English. Possibly also from Icelandic and Spanish.

If you want me to do this, please tell me how to post my translations. I have noticed that some bands include a translation below the original song lyrics, would this be a good idea to do even if my translations wouldn't be official?

I don't know whether there is an official policy but we normally only have official translations of lyrics here. I believe to also have seen a couple of user made ones, though.
I'd rather recommend you to add your translations to a website dedicated to such translations, for example this one: http://lyricstranslate.com/
That way it's also easier for you to get feedback on you work.