[...] With regard to the status of "Ubuntista", although words ending in -a in
the Latin languages are normally feminine, [...]
It seems very hard to come up with a word that isn't gender specific in _any_ language. To change the term from "Ubuntero" to "Ubuntista" makes the term sound very much feminine in Swedish (Inga, Ulla) , the other Scandinavian languages, German (Hanna, Lena), Russian (Alexandra, Jana), etc.
It seems that in some languages the ending -a indicates feminine, but as mentioned above in Japanese -o is feminine. I think that whatever random name that is chosen it will be gender specific in some language and perhaps the fact that it's been successfully used for four years indicates that the current name is rather good.