Just one comment that merits repeating here:
The faithful's ability to speak or understand Latin is really a marginal and insignificant issue in analyzing the value of Latin in the liturgy and the life of the Church. In fact I would argue that it is precisely because it is not understood by most people that it should be retained in the liturgy and in the Church.
And this is why i object to this priest's opinions because he seems to want to advocate for the restoration of Latin for it's own sake (as a living language) which is not really an important task for the Church, Latin is only a tool which has served the Church exceptionally well for the purposes of unifying the liturgy, maintaining doctrinal clarity, and connecting the present with the past. He seems to not care for these functions, as shown by his attitude to the old mass and his negative remark on medievalism. So clearly he has another agenda that is not at all consistent with a truly catholic perspective.
And one question:
Why are people so hung up on the issue of needing to understand Latin?
I fell in love with the Latin Mass even before I ever saw one, I just heard about it and looked at the pictures inside an old missal. It never occurred to me that it would be problematic spiritually or intellectually because I saw it as a way of uniting the faith, maintaining doctrine and connecting with the past, clearly more important objectives than whether i can understand it, besides I can always read a translation.... In this way it seems more about convenience for the audience than what is good for the Church itself.
I think that the issue of language in the liturgy is only relevant these days because we have bought the idea of the protestants that worship is primarily for us.... the mass and indeed all worship is for God Himself. It is worship not instruction and so we do not need to understand and hear every single syllable. If we are so curious we can read a missal, discuss it afterwards or read a book.