This isn't just a translation issue, it's also a cultural-attitudes issue as well. Why do we even put sexual preference as one of the primary line-items on your profile? For the US (or at least US college undergrads), this makes sense: it's relevant information that you want to share. But when you take it international, it may not be relevant, or may not be something you want to share. There are a few countries where homosexuality still carries the death penalty, quite a few where it's far more taboo than the US, and plenty of other ones that practice arranged marriages instead of open dating. A social networking site created in countries like those would never consider putting dating preference in their profiles at all, much less how to phrase them. Even if the phrase were translated appropriately, it wouldn't make sense to ask it.

Considering that, it's probably better to leave it open to local interpretation.