I guess these cult folk rely on the fact that most are ignorant of History so can recreate facts on the fly.
You know as well as I, if not better, about the Social make up and culture of the Roman Empire. Multilingual was common, if in no other form but basic day to day communication.
Peter crossed the Empire beyond the Eastern Frontier and back all the way to Rome as multiple historical sources note. He lived for years at the very crossroads of the Empire. To even begin to think he knew no Latin is past absurd and borders on insanity.
I know it and have not even seen one of Mel's movies.
Anyone with even a rudimentary (read High School) knowledge of Roman History knows that multilingual (at least to a minimum level of understaning) was not only common, but necessary.
Even more so for the commoners, as the elite (Roman citizens and government) would expect their ‘lessors’ to learn their language rather than the other way around.
The educated Greek slaves were often the tutors of the elite Romans.