I was learning Cantonese so I would finally be able to talk to my Grandmother and some of my relatives.... but I gave up. Cantonese is by no means a dead language, but Mandarin is much more, well, shall we say.... important. And although both Mandarin and Cantonese are difficult languages, Mandarin has 4 "tones" while Cantonese has 7, some of which I can't even tell apart no matter how hard I try.
Learning new languages is moot however - in 10~15 years, we'll have instantaneous computer translation of both aural and written communication. I'd say in about 7 to 8 years we'll have computers that can understand human speech just as well as any human, and even now Google Search does a pretty damn good job of understanding what I'm saying to it. Google Translate and Language Tools work quite well for Spanish and French, and it's not too shabby for German, although it still has immense difficulty with Asian Languages.
But it's doable. I'm confident on that point - we will one day have machines that can translate, virtually perfectly, any text in any language to any other desired language. US Soldiers in Iraq are already using devices that can translate well known phrases from English to Arabic.
I'm not going to bother studying another language, because in 15, or at most, 20 years, I won't have to. I'll be able to talk to anyone on the damn planet.