You need to know about a book by Loraine Boetner, Roman Catholicism. Boetner was a Protestant apologist who wrote this book for the purpose of attacking the validity of the Catholic Church. Unfortunately, his method of argumentation relied heavily on – to put it charitably – demonstrably incorrect accusations and fundamentally inaccurate descriptions of Catholic doctrine (e.g., he claims that the Council of Valencia forbade the Bible to laymen in 1229, even though there was no such council; he claims that the Mass is a “re-Crucifixion” of Christ; etc.).
One of his allegations is that the Church “imposed” the Latin language in 600 A.D. His point was apparently to make his readers think that the Church was hiding the liturgy from the common people (you know, because Latin is hard). The problem with that claim, of course, is that Latin was widely spoken in Europe at the time, so holding the liturgy in Latin would not have prevented the people from understanding it.
A similar argument is often made that, in Europe during the Middle Ages, the Bible was only kept in Latin. Although I believe that factual statement to be false, it would not matter if it were true: Protestants who make this complaint apparently always forget that, in Europe during the Middle Ages, everyone who could read their own language could also read Latin.
The thing is, Boetner’s “scholarship” has been disproven time and time again. But certain anti-Catholic apologists keep printing and disseminating it, even though they clearly know by now that its claims are false. So Catholics keep encountering these comments over and over again and having to refute them over and over again.