[a humble lich]

I'm not sure I'd say superficial, but more that the founder of Megalos was specifically modeling his new empire on the Roman Empire, and the Byzantine Empire was also "modeled" on the Roman Empire. (In their case it wasn't modeled on Rome and more was the surviving continuation of Rome.) So I think there are some real resemblances, but no direct connection.

As for languages, I would suspect that Anglish has borrowed even more words from other languages than modern English has. After the Banestorm there were large groups of people speaking many different languages which were thrust together all of a sudden. I would imagine some form of creole would soon develop, which eventually evolved into Anglish. But given that there were originally many non-English speakers amount the Barnstorm victims, I would imagine that those people would have left a linguistic mark.

I had thought that the book also says that there are small isolated communities where other Earth languages have survived; however, I can't find where it says that right now. But it makes sense. If there was a entire village of Basque speakers taken by the Banestorm, they would probably still speak a descendent of Basque, and then also speak Anglish to outsiders.