As I have a lot of friends in Facebook that I assume do not share the same language preferences than me (they are from around the world), this feature had made think about how hard internationalisation can be... I'm pretty sure than translating all the possible options, plus pronouns, etc, will be an interesting problem ;-)
PD: I've checked and the option is only available so far to users using US English interface, so not a problem currently. I can imagine it will be at some point.
Proper internationalization [1] is really hard. Seems like Facebook has done a great job though. The documentation [2] for this feature points out that if you choose "custom" gender, you need to choose your preference for male, female, or neutral pronouns.
[1]: Heh, I'm so used to typing i18n, that was weird to type out.
PD: I've checked and the option is only available so far to users using US English interface, so not a problem currently. I can imagine it will be at some point.