You've already ticked English and Yoruba. Wherever you get deployed to, as far as you have interest in learning the language, I'm pretty sure you will learn it. Learning languages is not really a big deal. It gets easier when you are in the midst of people that speak the language casually. You also need to be willing in order to do so.
In my case, I don't see myself learning any other Nigerian languages. The ones I know are enough. Haha.
I hope you get a favourable posting during your NYSC.