This man was a famous Professor of Latin at a prominent university such as Harvard, Yale, Oxford, or Cambridge. He was born ~90 years before into a “royalist” family in Budapest, Hungary and he was raised speaking Latin and I’m not sure what else as a first language. Both of his parents spoke Latin and Latin was the usual language of the home. He said that around 1850 in this part of the Austro-Hungarian Empire, Latin was still fairly widely spoken as a native language among this very wealthy elite cohort of people with royal blood. Perhaps they lived in castles, who knows? You may be able to find more on him in Wiki.
I know that ~1850, in Zagreb, Croatia, if you went into a bookstore, most of the books would be in German and Latin. Few people could read and write then, and Kaykavian was actually the official language of Croatia as official “Serbo-Croatian” – really Shtokavian – was not even created until decades hence by Vuk based on the Shtokavian dialect of Eastern Herzegovina. The academic journals in this part of the world, especially the former Yugoslavia, to this day often have Latin names.
Latin is the official language of the Vatican, but I think it is only used for writing. I’ve heard it’s not spoken. Also it is only learned as a second language there.