I am based in South Africa. If I set my common names to local, I get a spotty mish-mash of English and Afrikaans, but not formal Afrikaans names, folksy ones like Jan-tarentaal rather than Gewone Tarentaal. I’d prefer South African English names if possible, but I don’t seem to be able to enact that…
Unfortunately this can not be fixed unless the different language communities agree to use different geographies for their entries. As long as both communities do entries under the same place, or the ones already entered are standardized, you will see a mix.
Many of the English names have been set for place “Southern Africa” (rather than South Africa), so if you try that place instead, you might get better results.
See related feature request: https://forum.inaturalist.org/t/select-language-for-common-names/5430
(and welcome to the forum :)