The thing is, if you hate your thesis, if you aren't interested in it, you're so much less likely to finish or produce a good piece.

Seconding this. I never would have made it through my honors thesis if I hadn't been passionate about the topic. Write about something you're excited about.

I would also suggest talking with professors about your language concerns. For an undergraduate thesis, it's likely they won't care whether your primary sources are in translation or not.