Although changing text is an option, it will only change the current locale. It would be useful to be able for plugins, themes or theme components to handle custom locales as proposed in the OP. Is there such a functionality?
In French, one could use « usager » instead of « utilisateur » or « utilisatrice » which brings back a meaning that disappeared recently where « usager » – meaning someone you serve with respect and attention – was superseded in public transport with privatization: now privatized transports prefer to use « passager » (passenger) or even « client » (customer). This is a small semantic shift but it means a lot, and in languages that can make a difference between users/utilisateurs (what is using the program) and people/usagers (who the program is made to serve), it can very meaningful to make the effort from an intersectional perspective.