At school I learnt some French and German - German to Standard Grade '1', and French to Higher grade 'B'. I didn't do anything with languages when I did my first degree, but when I was doing my PhD, I did two terms worth of German lessons at UCL.
French - I've always found French much easier and reckon I could become reasonably good at it with some effort, but in terms of business use, it is second to German (sorry froggies!). It would be easiest for me to learn, but least satisfying.
Scandinavian - When I went to Oslo for a weekend with Kev, I learnt so much Norwegian that I was able to convince some locals that I was actually Norwegian, but putting on a funny accent (and wearing a hire kilt when it was -20C, but that's another story...). I've always thought Scandinavian languages sound 'cool', but a) Scandinavians tend to speak near perfect English so there is no need to learn it, and b) there's not much point in learning it unless you will be living there.
Mandarin - Apparently there are quite a few Chinese around, and once they have conquered the USA in WWIII, we will all be required to speak Mandarin...or something like that. Seriously though, it is supposed to be becoming very popular to learn, because the importance of China is increasing as it's economy develops. I've never learnt a word of it and I'm sure it would be difficult, but I do remember being impressed by a certain Swedish friend speaking very passable Mandarin.
I quite fancy doing an MBA one day. If I wanted to do it in a European country (other than the UK), I would need to speak another European language properly, so I do intend on trying lessons or something again.
But which language should I learn? I have put up a poll with the four options - German, French, Scandinavian (Norwegian/Danish/Swedish - that would need another poll), or Mandarin.
Which do I learn? You decide!
Of course some might say I should try and learn English first!