I'm on the project as the developer, working for the client, and didn't have time to do the UX portion, so that was farmed out. So, we just got wire frames in from the digital agency and they're pushing back on having the language toggle visible. They want it buried in the burger menu.
When I asked them if they felt it was good usability to force a user to find the language toggle on mobile, they avoided the question.
I've done some research, and asked some UX friends, but I'd like a lot of other opinions.