I think the reason why the request was denied in the past is because all of the Nigerians On Bitcointalk speak English and admins probably didn't think a Pidgin English board would have many users. But if the number of Nigerians is much higher now, it makes sense that you guys have your own local. However, if your local would allow users to write in English as well, the admins might turn down the idea. A Pidgin English only local would have better chances.

Discuss among yourselves how you would like your board to look and what sub-boards it should have. That helped the Croatian community get new sub-boards a few months ago. Those ides were then presented to theymos and Cyrus and the new boards were created.   

I think it could help to see how many Nigerians there actually are and how many of you are active on Bitcointalk.If the numbers aren't as high as they should be, maybe an African local could be an alternative option. In that case, you have to agree on which local languages would be accepted.

Good luck with the request!