I can tell you how one such board is structured: The Spanish local board.
Spanish is vastly spoken by people in Spain and latam (with some wording differences). As such, the local board is the same for all, although there are four inner marketplace subboards that are based on a geographical areas.

Spain itself has more than one official language (some regions within officially have two languages), being the main official languages Catalan, Basque and Galego. These three bear their own thread in "other languages/locations", and are not currently defined as subboards within the Spanish local board. It is therefore essentially language based, not geographically.

That does not mean that all language situations need to follow the same pattern. Nigeria’s official language is English, but it seems a pretty complex country on the whole in terms of languages (see https://worldpopulationreview.com/languages/nigeria). I figure that a strong cultural common background and geographical area, and a demand from many members could constitute a valid candidacy to consider, whatever the outcome.