"I think it had more to do with the fact that with Latin as the 'universal' language, it didn't matter which peoples were converted, or their native language, the Mass would be said in the same language everywhere, and folks in other countries wouldn't have to chance to put their own 'spin' on the Word of God"
I'm sure you are correct, but unfortunately, most weren't educated enough to know Latin.
Many were educated only enough to know the Latin for Mass, though the peasants, I'm sure, were just supposed to sit and listen, and pick it up after a while.
The Church didn't switch to Mass in the Vernacular until I was ten years old. Prior to that, we each had little Missals (books), which were usually received as gifts at First Communion, around age 7. Each had the English on one page, and the Latin on the facing page, so even if you didn't really know much Latin, you could still understand what was going on at Mass. Even now, after 42 years, I can still remember and sing some of the hymns in Latin!