Even back in the “old days”, the missals presented a Latin/vernacular form. Latin/English, Latin/German, Latin/ French, etc. etc. So we ‘understood’ what was going on in the Mass just as well (if not better) than we do today.
Because as somebody noted on another thread, if you go to a vernacular Mass, you are not always going to get ‘the same words’ that you do at a traditional Mass. It’s actually easier to know that “dominus vobiscum” is **always ** going to be “the lord be with you”, for example. . .whereas you might hear anything from “the lord be with you” to “the greetings of God be with you”. . .“we welcome you”, “in the name of the Creator etc.”. . .because a lot–a LOT-- of priests try to make the Mass more ‘interesting’, more ‘personal’, and you know (before you start to flame, please) that there is
some latitude which is permitted. As in, “the priest says these or similar words”. . .rubrics which are found in one or two places in the Mass but which in the practice of at least one priest in my diocese wind up in him changing almost every single word in the mass.
As another poster noted as well, familiarity with Latin (with any ‘other’ language actually than one’s primary language) is for the vast majority of people extremely helpful. It enlarges one’s vocabulary for one thing. It broadens the mind. For the very, very few for whom even ‘one’ language is difficult, once again I point out that today we have missals which explain in the vernacular; just as we have ‘sign language’ for those who are hearing impaired; there are tools out there to make the Mass as intelligible as possible. Latin will not make it ‘less’ intelligible as the use of Latin does not abrogate the use of a vernacular language; instead, it enhances it.
My current parish is Polish and while I do not understand the language, the congregation sings some hymns in Polish and occasionally the Vespers service is held in Polish, for example. I don’t have any trouble listening to a language I don’t understand (the hymns are NOT translated, but I can sometimes figure out if it’s a familiar tune like, tantum ergo

,) and I have noticed that once I’ve gotten familiar with the sounds and correlated them with how the words look on the hymnal, I can recognize them in other songs and begin to gain a sense of the language. So I’m not just listening to ‘mumbo jumbo’, even if I don’t know the tune or words at al at first; I’m just starting on the long process of learningl. These words mean something to a lot of the people, and I’m learning too. It is a very positive experience–far more positive than you might expect–humbling ‘not’ to know something yet exciting to learn, however slowly. It makes me feel a part of a bigger whole.
I think that people have good intentions but that they really do not realize that having more Latin in the Mass is such a positive experience. I truly think that focusing on negatives, as if by ‘thrusting’ a ‘different’ language on people we are
depriving them or making it too
difficult for them, really is kind of saying that people are too stupid or lazy to be bothered learning, so why even try?