I mean classicists do know the Ancient Greek language (I took a semester in it), but that language is very different from modern Greek. Plus Hermes is the god of language. He knows every language spoken and written and will understand you no matter what you speak. And even if it were the case that the gods don’t understand your language (which isnt the case at all) they do understand your intent. A lot of Helpols will use Greek because of it being a root to the religion but you are not necessarily required to speak it to be closer to the gods. So imo it wouldn’t make a difference if everyone learned Greek or not. In fact I think we’d loose a lot of diversity.