If the board is spam, it will be muted, locked. Locals can continue their spamming before the board is locked.
Use report to report spam posts because it's responsibility of local members who ask for the local board.
The board is in English and global moderators, current moderators who can use English can moderate it. All moderators in Bitcointalk can use English well and all of them can do this.
I think it's a great idea to get local moderators to moderate the board. Despite that the board uses English language as a language, it also uses what we call the Pidgin English. Pidgin English is a lingua franca that is a mixture between English language and other African languages. Pidgin is widely spoken in Africa and every country in the continent has its peculiar style of speaking in Pidgin. For instance, the style in which a Nigerian speak Pidgin English is different from Ghana or Cameroon despite their closeness in borders.
Nigerian Pidgin is blend with other major indigenous tribes in the country such as Hausa, Yoruba and Igbo. So, most at times, it takes an indigenous speaker to understand the conversation between them and communicate. Likewise, it will take a local moderator to be able to effectively monitor the conversations in the board as well as sort the threads in the proposed child boards.
An English moderator is not a bad idea but for a more effective moderation of the board, you need a local or native moderator.
You have spoken well and provided further explanations for better understanding. When it comes to selecting a moderator for a board or sub-board, there are pros and cons to consider. You need to trust who you are selecting and how well they have contributed to the development of the local board. Additionally, it should be someone who is not afraid to speak out, preferably someone with a history of addressing issues they believe are wrong or not handled properly in the local board.
Having a local moderator is more preferable, as you mentioned. The person should be fluent in both good English and African Pidgin and should be able to relate to African culture, beliefs, and a way of life. Time zone is also important. It's best to know the moderator's available hours for moderation.