On the website, sure, but I don’t think the app has that support. Looking at the settings options for the (US-based) iOS iNat app, there’s not an option for changing the language to something other than English. Furthermore, it seems that changing language settings on the website in profile settings doesn’t change the language on the iNat app. Given that a lot of users are primarily or exclusively using iNat content through the iNat and Seek apps, other languages should be an option (which has been requested here).
If it’s doable, being able to see common names and such in two languages at the same time (which I think is what johnmontgomeryrouse was getting at) would be very cool, for both the multilingual and the trying-to-be-multilingual among us.