I've blogged about this briefly before; now, thanks to some very generous help from various Latinists, I can present the whole thing in English for the first time online. It is particularly important to keep in mind the consistent teaching of the Church on issues like this, as expressed in proper magisterial documents printed in the Acta Apostolicis Sedis. They can be ignored, of course, but they don't go away.
This document is referred to repeatedly by Bl. John XXIII's Apostolic Constitution Veterum Sapientia (1962). Its importance lies not only in its content, but the fact that as an Apostolic Letter it is an act of the Papal Magisterium; many documents on this topic are Instructions, which are of lesser weight.
Most of these documents are not primarily concerned with the liturgy; Officiorum omnium doesn't even mention it. The concern is with Latin as an irreplacable foundation for a seminary education, opening the door to an immediate engagement with the Latin Fathers, the documents of the Church, Canon law, and an enormous body of theology, history, and literature.
For more on Latin in Seminaries, see the FIUV Position Paper 12: Latin in Seminaries.
Officiorum omnium can be downloaded in full here; below is a key passage.
Since Latin is such a language, it was divinely foreseen that it should be something marvellously useful for the Church as teacher, and that it should also serve as a great bond of unity for Christ’s more learned faithful; that is to say, by giving them not only something with which, whether they are separated in different locations or gathered into one place, they might easily compare the respective thoughts and insights of their minds, but also – and this is even more important – something with which they might understand more profoundly the things of mother Church, and might be united more closely with the head of the Church. It is clear that the clergy should, in advance of the rest, be very studious of the Latin language for both these reasons, not to mention others; for we do not here run through the estimations by which this kind of speech is recommended, that it is compact, rich, rhythmic, full of majesty and dignity. And you might say with wonder that it was ready-made to serve the glory of the Roman Pontiff, to whom the very seat of Empire came as by a bequest.
But if, in any layman who is indeed imbued with literature, ignorance of the Latin language, which we can truly call the “catholic” language, indicates a certain sluggishness in his love towards the Church, how much more fitting it is that each and every cleric should be adequately practised and skilled in that language! It is certainly their task to defend Latinity with all the more steadfastness, since they are aware that it was with all the more violence that it was attacked by the adversaries of catholic wisdom who in the 16th century shattered the accord
Europe had in the single doctrine
of the Faith.
Therefore – and this is something guaranteed by canon law (Codex Iuris Canonici can. 1364) – in the schools of literature where the sacred order's expectations reach maturity, we wish the alumni to be instructed very exactly in the Latin language. We wish it also for this motive, in case, when they later approach the higher disciplines that must certainly be both handed on and received in Latin, it happens that through ignorance of the language they cannot achieve full understanding of the doctrines, let alone exercise themselves in those scholastic disciplines by which the talents of youths are sharpened for defending the truth.
Thus the occurrence we often grieve over will happen no longer: - our clerics and priests, when, through neglect of the copious volumes of the Fathers and Doctors of the Church in which the dogmas of the Faith are presented, being both set forth very lucidly and defended invincibly, they have not put enough effort into the study of Latin literature, seek for themselves a suitable supply of doctrine from more recent authors; among these one can virtually say not only is a clear kind of speech and an exact method of arrangement generally lacking, but so too is a faithful interpretation of the dogmas. So it was that Paul warned Timothy: “Hold the form of sound words… Keep that which is committed to thy trust, avoiding the profane novelties of words and oppositions of knowledge falsely so called; which some promising, have erred concerning the faith” (2 Tim 1.13, 1 Tim 6.20,21). These words, if it were ever otherwise, are in these times especially relevant, since all over the place so very many have become used to hawking various erroneous fallacies, masked under the name and pretence of science. But who could show up and refute these fallacies without thoroughly mastering the understanding of the dogmas of the Faith and the force of the words in which they are solemnly expressed, in short without being skilful in the very language the Church employs?