Achieving a decent level of proficiency takes thousands of hours and it's nuts to invest that kind of time in anything that you're not excited about. Acquiring the ability to even stumble along will take hundreds of hours.

You need a reason to want to learn the language, but it doesn't have to be a good one -- only something that you find sufficiently compelling. Maybe you've just been fascinated with the place where people speak that language and want to travel there. Maybe you just hope to impress some girl. If you're interested in a particular subject where many of the best people speak a particular language, that's a good way to go. But definitely don't pick one until you know.