IMO, you have to have a reason for the language. Mine is that I wanted to read and watch anime/manga/tv/books/games that weren't being translated. Of course, these days they're all being translated faster than I can read them. But it was enough to get started, and I definitely enjoy them more than if I didn't know the original Japanese, too.
But I've tried to learn other languages that I don't have a use for, and I've found it nearly impossible. There just isn't enough motivation.