See https://en.m.wikipedia.org/wiki/Special:ContentTranslation for example.
Looks like an issue with MobileFrontend dependencies.
CXStats has similar issue but seems to work still.
Was this reported because Content Translation was inaccessible from URLs that have mobile subdomain? Or because there were no responsive features added in T157212 and other tickets?
I believe some JS modules were not marked for mobile. It works now.