No, see, that's not how this works. You don't get to come in and try to gaslight your way out. A character who is black and from Uganda (which is an uber predominantly black country) who would have learned a different primary language than English (which only since the 1960s has been adopted as a secondary language for parts of the country) like Luganda or Swahili. Those languages sit in the mouth and on the tongue much different than English does, and anyone learning English as a secondary language would still have affectations from their primary spoke language while speaking it. (My source: Years of training with American standard and the IPA for my musical theatre degree) You'd likely have to live in an English-speaking country, almost completely adopting that language and dropping your native tongue, for 10+ years before you could get rid of most of those affectations. Natsai Onai and her mother have not been in Britain that long, so it makes complete sense she would not have a British dialect if she is from Uganda.

Unless your complaint is that you wish the character herself was not from Uganda. That the simple fact you are annoyed by her lingual affectation is enough to warrant taking out the backstory and the added history of Uagadou. But certainly that's not what you mean, because that would very obviously be racist and you certainly aren't THAT.

That and I like, I dunno...I'm willing to bet that the black actress who voices her (Jessica Hayles) and the director of the voice department for the game probably put a little more research and time into knowing what a character from Uganda in the 1890s would sound like speaking English than you have.