I wonder if there's enough meat on that topic if you broaden it out to "How to make your NPCs distinctive without using weird accents"

Instead, I try to differentiate based on tone, cadence, word choice. The streetwise guide talks faster, more idiomatically, and with a less sophisticated vocabulary than the scholar who chooses her words with care to convey exactly what she means no more no less

7/7

I feel like the question of doing accents or 'voices' is very much centered on games either set in modern English-speaking settings or generic Europeanish Fantasy. When you go outside that narrow range, I'm very leery of trying to do accents.

I also don't trust myself to do it right on the first take every time. I am not that good - and I'm not on Critical Role so we don't get multiple takes because we have a whole day in a sound studio.

I could do a whole bunch of research on what modern Malians sound like speaking English, but that lands wrong. It would probably sound stereotypical or mocking. It also doesn't convey how these people sound in context. Their accents don't mark them as outsiders, the PC's speech patterns do.

I'm currently running a game of Exalted 3e being recorded as an AP. Set in Origin which is basically Timbuktu with a light coat of fiction. There are ethnic groups that are 1:1 mappable to Real World ethnic groups. And I'm not doing accents for NPCs for several reasons.

I have done accents as a player, sometimes as a GM. But as a GM, there are some minefields out there when it comes to having a diverse cast of NPCs. You are running a game in 1930s Egypt? Great - but I don't want to draw on media representations of accents for that. Africa? No.