Considering how popular bitcoin is in Nigeria despite not so friendly government I am glad to see that you decided to ask for your own local board and it's an important first step but I think that you will have to increase your activity in
Nigerian Bitcointalk Community Hangout in order to have real chances of getting your own board. Considering how many members you have that are active in English part of the forum, that shouldn't be an issue, you just have to encourage them to be more active there so you show forum staff that there is a real need for local board and that you "outgrown" the thread started by @CryptopreneurBrainboss.
I wanted to support most active communities without local boards so I included them (starting from October 2020) in
monthly overview of the local boards activity so you can see how Nigerian thread stands compared to others.
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.
As explained to me by one Indian member, reason why Indians use English language in their board is very simple: they have 22 official languages and it would lead to chaos if they start opening sub boards for each of them. Using English is more elegant solution, but that also probably discourages some from being active there.