Latin is still the official language of the Catholic Church. The meaning of words in dead dead language like Latin don't change much and so a document written in Latin is likely to be easily understood in 4-500 years (for people who can read Latin) and used for translations into the local vernacular. Whereas a language like English is constantly evolving and so the version of some words in, for a relevant example, the original King James Bible, do not mean the same thing in modern English that they did in the early 17th century.

The hulabaloo about the Latin or so-called Tridentine Mass is a cultural issue that is mostly about shifting societal norms and only incidentally about it's being in Latin. This is evidenced by the fact that the current form of the Mass, the Novus Ordo, is written in Latin then translated into the vernacular, and it can still be validly performed in Latin without special dispensation from the Vatican.