Whenever I've been motivated to "change the world" by coding, particularly Open Source, I've picked some language like PHP, Java, Javascript or Python which was mainstream, mature and commercially in demand. If you're trying to work in a language like Haskell you are probably going to waste a good chunk of your time "reinventing the wheel" writing libraries that you can just get out of a repository for a mainstream language. If you're doing something that's really hard it's not a good time to be learning a new language and learning the hard way "why more people don't use language X?"
On the other hand I try pretty hard to never say "Cold Fusion" or "Microsoft Sharepoint" in a public forum because that attracts truly desperate recruiters.