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.

You can't deny it, mass is much more stylish in Latin ;)

Historically Latin was also a common international language. Educated people could understand Latin across much of Europe. Not so great for the majority of people, of course. The article seems to indicate that in some places it was pretty widely understood.

I think some rites of the church did use other languages such as Syriac.

I knew about SSPX but not the Palmarians. They seem to be even odder and a cult. Interesting in the same way I find conspiracy theories interesting, so thanks.