text: Obviously, Catholic worship was always in Latin.  Jesus must have used Latin at the last supper.  Otherwise, at some point, mass was changed from some other language to Latin, which would have been a concession to some modern, for its time, practice.  Since we know all change from original tradition is bad, there could not have been a time when the mass was said in anything other than Latin.  Otherwise,  our sincere devotion to the Latin mass is merely a devotion to some man-made practice which only became tradition over time because it was repeated.