40-50% of Africa in 1900 as part of the third UHV goal.
I think this is basically all of Coastal Africa. Keep in mind that an enormous amount of the landmass is Desert and Jungle and Marsh in game, none of which can be settled and which takes an enormous amount of time for culture to spread over.
Take the following map as what France historically colonized (France in light blue):
Spoiler France Historical Colonization :
In terms of what can be settled in game, you basically only have the Maghreb, West Africa, and Madagascar, with perhaps a city around Lake Chad. You'd be lucky to get 20% of Africa out of that.
North African lands are NOT useless.
With all respect, North African lands are useless. At best you get 4 - 6 improvable land titles per city, and then they compete with other Mediterranean cities (in cores) for sea tiles. Everything west of and including Tunisia are decidedly third rate cities, and perhaps some of the worst France can go for. There's simply too much Desert and Peaks in these cities for them to ever be good.