An initial selection of locale should auto-populate the common names language. I would imagine it would then first prioritize the common name language (aka “lexicon”) and second prioritize the place.
Common name place should only be necessary to assign when there are conflicts between areas that speak the same language but use different names. It shouldn’t be necessary to enter the place in every time, i.e. as is now, for languages the website isn’t translated into, or for people who speak one language but prefer to use common names in a second language.
This is an important setting to further iNat’s mission among an international audience. All language settings should be available online and on the mobile apps.