I suspect the German Empire would largely keep extant names. They weren't too twentieth-century about these things. Even the German names tagged on to Alsatian, Polish and Russian towns were largely traditional (Germans had lived in these parts for centuries and had their own nomenclature). Some names lend themselves to translation (Kapstadt is one), but mostly, the transliteration would be the only thing to change. In the case of English or French names, probably not even that (Wilhelmine Germany may not have liked them, but respected them as fellow imperialist loot.. erm, Kulturvölker)
So:
N'Djamena maybe Endschamena
Faya-Largeau maybe Faja - Lascho
Cape Town - Kapstadt
Durban - Durban
Bloemfontein - Either Bloemfontein or Blumfonteen
Luanda - Luanda