And yet:
The Council of Trent already recognized the great catechetical value contained in the celebration of Mass but was unable to bring out all its consequences in regard to actual practice. In fact, many were pressing for permission to use the vernacular in celebrating the eucharistic Sacrifice; but the Council, weighing the conditions of that age, considered it a duty to answer this request with a reaffirmation of the Church’s traditional teaching, according to which the Eucharistic Sacrifice is, first and foremost, the action of Christ himself, and therefore its proper efficacy is unaffected by the manner in which the faithful take part in it. The Council for this reason stated in firm but measured words, “Although the Mass contains much instruction for people of faith, nevertheless it did not seem expedient to the Fathers that it be celebrated everywhere in the vernacular.”(GIRM 11)
This is quoting the Council of Trent, Session 22, Chapter VIII:
Though the mass contains much instruction for the faithful, it has, nevertheless, not been deemed advisable by the Fathers that it should be celebrated everywhere in the vernacular tongue. Wherefore, the ancient rite of each Church, approved by the holy Roman Church, the mother and mistress of all churches, being everywhere retained, that the sheep of Christ may not suffer hunger, or the little ones ask for bread and there is none to break it unto them, the holy council commands pastors and all who have the cura animarum that they, either themselves or through others, explain frequently during the celebration of the mass some of the things read during the mass, and that among other things they explain some mystery of this most holy sacrifice, especially on Sundays and festival days.