No one would accuse Pope St. John Paul II of being a traditionalist. But even he liked to use Latin sometimes.
John Paul II lived most of his life as a Catholic prior to the liturgical reforms that followed the Second Vatican Council. So unlike many clergy today, he knew Latin well (among the roughly dozen languages he knew).
It’s not completely clear what the precise context is of the video below. The video title says it is from 1982, and it appears to be a Mass celebrated in St. Peter’s Basilica.
But in any case, it’s pretty cool to see John Paul II lead the congregation in singing the Lord’s prayer in the traditional language of the Church!