On Stack Overflow in Russian, I clicked on the "Follow Post" button on a question, but I did not have an account there. The popup that contained the "Join" button was mostly English, not Russian; only the community name and Join Community text was in Russian:
I noticed this also when I joined Stack Overflow en Español, and it happened when I joined Stack Overflow in Portuguese:
Can we please add these strings to Transifex? It seems a little counterintuitive to have the "Join Community" strings in English on a site made specifically for another language.