I don’t think Latin was ever considered a sacred language; but it was the Lingua Franca of Europe for many centuries. The Mass was conducted in Latin in the same way that all scholarly discourse was conducted in Latin, and all academic papers, treatises etc (for example, Isaac Newton’s Principia Mathematica) were published in that language
In nomine Patris et Filii et Spiritus Sancti. The Trinitarian formula. Latin is the official language of the Church. It is considered a 'dead' language, not given to any change.