Fluent in Russian and English here, so- expert? I will happily translate Russian phrases. Yes, you there, English speaker with Russian mafia characters speaking peculiar, broken Russian in your stories- I see you! x')
Also only confident with basic French, since I am not a native speaker, and don't get to use French as often as I'd like, outside of reading/watching movies. Since my comic contains French phrases/interjections, I may actually be looking for a French-speaking beta-reader down the line.
Good luck with your Spanish translation! (I agree with @joannekwan -this is an awesome idea for a thread)