If I could pick any language to learn, it would be Russian. But I had to settle for French, and now I'm on my 4th year of learning it. It's not great, but it was either that or Spanish, and I'd rather not encourage the Mexicans.
toé, mon `tit morveux, tu pourrais v`nir au Quebec, le! Sa s`brasse, icite pis c`est l`fun. Pis si tu vas à Montréal, t`es un estie d`con!
So yeah, that`s the french of a certain part of Canada... me, unfortunate soul, I had to learn this when I came here. I`d sworn to never learn French, et voilà(not to mention how much frustrating it is to fiddle with my keyboard`s settings just to get all them accents right).
Like already mentioned, French is one of the official languages of the UN, is spoken in a good part of the world(except in Quebec, that`s not French ), so if you know it, you know one more useful thing. I would also second the suggestion to learn Mandarin. Personally, I have only Arabic and Mandarin left and I`ll be functional or fluent in the top six of most influential languages in the world. Considering the range of people I can speak to in their native language, learning one more is always a good idea. And the list of languages I want to learn for fun is even longer