One of the articles mentioned inscriptions in Coptic, Latin, and Greek. The elites would have spoken both Greek and Latin, I think? Greek was commonly known and used. Caesar, a Very Latin Roman, as he was being murdered in Rome, is conjectured to have spoken Greek to Brutus, another Very Latin Roman.

The notion that people are mostly monolingual, and that language is very closely tied to a cultural identity, is a modern projection (and far from universally true nowadays as well).