Incidentally, even at a Latin Mass, the Bible readings are in English (or whatever the local language is).
BTW, in the Fourth Century Roman Empire, the local languang was ... LATIN! For which reason the Church had the Scriptures translated from Greek, Hebrew, and Aramaic to ... Latin.
I have never before considered your point that the amount of Latin knowledge would have been small for the mass compared to the amount needed for reading the Bible.
However, converts still have to learn some new language if they wanted to worship God in a Latin mass. Perhaps this is why Vatican II decided to change...perhaps too many Africans and Asians converting and not liking that they were not able to comprehend what they were saying?