Giving the mass in Latin wasn't (generally) done because people understood Latin, but because of a traditionalist sense. The Second Vatican Council stated (among other things) that the mass could be done in other languages apart from Latin, and that it was a good thing to use local languages, so people could understand it better.

After that Council some excisions appeared, like the Society of Saint Pius X, that reclaimed the old ways of giving mass, in Latin, (and, IIRC, with the deacon giving his back to the people, not looking at them), and said there was "a moral and theological crisis in the Catholic Church".

Or people like the Palmarian Catholic Church in Spain, saying they have the authentic Pope, and the one in Rome is an Antipope. They were a scam for pulling money from their believers, and their "Pope" kept spending money on booze and expensive cars. They still exist.

The church Latin used in “the Latin Mass” is relatively simple and pretty easy to learn; and it’s very rare to find one that does the readings and homily in Latin; most of those are in English (or the local language) even at an FSSP parish.

Of course if it’s “really” done in the ancient way then it’s done at such a high speed that you need five or six Jesuits and advanced recording equipment to even figure out what is being said. ;)

Latin was the standard language of the Roman-Catholic Mass until the Second Vatican Council in the 1960s. The current form of the Mass in national languages was formalized in 1970.