I'm not going to do a Finnish song simply because I do not speak the language.
When auditioning for a play or a musical, it is suggested that the auditionee NOT read from the script using an accent (even if the character has one) unless he/she can do the accent flawlessly.
I am applying this principle to auditioning for an established metal band - since I don't know the language, I'd rather have three good songs in english, than butcher one in Finnish. That wouldn't do anyone any favors. I don't want to make them want to stab pencils into their ears, after all. :P