I'm an MFL teacher these days doing German and French. I toyed with learning Spanish and/or Catalan so that I know when my girlfriend's family are talking about me but I'd rather not know. I've got a few friends learning/teaching Mandarin too, so I expect that's one on the rise in the next few within education. I did teach myself Dutch last year though as I was dealing with a lot of Dutch customers in my job and so thought it'd be good to be able to speak their language. Duolingo is still pretty good as an on-the-go type thing, I used that to help with Dutch. Some phrases it gives are a bit random.Memrise is fantastic though, I can't recommend it highly enough for learning useful phrases and sentences.