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.
I don't think there should be strict restrictions on what languages are allowed. Communication is key and if the community understands Common English (UK or US) as well as Pidgin English, then any of them can be used to discuss on a Nigerian board. The Indian local is run primarily using the English language, which is one of their national languages.
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.
A rough estimate could be drawn from the local thread linked in the OP. It's an estimate cause not every Nigerian who is active on the forum posts there or is aware of the thread. About broadening it to accommodate more African countries, that was how the local thread started, but majority of the interactions were from Nigerians, so it would not change much to make it a continental board.