Maybe naive or presumptive of me, but I assume that people who don’t speak English are mostly used to encountering English online and familiar with using translation tools. Sometimes I offer both English and Google Translate’s output (or my rough Spanish/Italian when possible). I wouldn’t want to assume that someone doesn’t speak English based on their username or location.
If you find yourself in need to someone who speaks a certain language, there are a few people who have volunteered to help here: https://www.inaturalist.org/pages/curator+guide#languages
See also this related feature request about adding an area on user profiles to indicate language preferences/proficiency: https://forum.inaturalist.org/t/indicate-a-users-preferred-language-s/2890