Rome Italy may have spoken latin, but, Latin was not the dominant language empire wide. Greek was the dominant language. Interesting isn't it - That even Paul's letter to the Church in Rome was written in Greek to ensure they'd understand it...
Your really talking about two completely different time periods here. The Vulgate antidates Pauls letter by about 330 years (look at how much English has changed in half that time). Can you give any evidence that Latin was not the common language circa 400 A.D. ? Every site I have found has said that Latin overtook Greek as the common language of the empire (not just Rome) around 350. A letter to Rome 350 years earlier is evidence that Greek was the common tongue (or at least the Church's common tongue) 350 years earlier. How does that bear on whether the Vulgate translation was or was not an "elites only" work of the RCC? These aren't RC sites, just a broad search for Scripture translations. Most of the sites I've looked at are Wycliff and Tyndale references.