What you’re describing is called decoding. Decoding is when you can pronounce what’s on the printed page. However, the Holy Father is requiring fluency, which means that you must be able to read and fully comprehend every word that you say.
This is not too difficult with those parts of the mass that never change. After a while, you have them memorized (ie. Pater, Sanctus, etc). It presents a challenge with the collect, because they change according to the day. Obviously, I would not even suggest that one try to read the scripture in Latin unless one is fluent.
I understand where the Holy Father is going with this. It’s not just a matter of clear pronunciation, you must actually speak the language, so that when changes come up, such as the readings and the collects, you not saying words that you don’t understand and you don’t have spend time with a dictionary or translation before the mass so that you know what it is that you’re saying during the mass.
He’s thinking about fluency like most of the people who occupy high posts at the Vatican, including him. These people are so familiar with Latin that they can pick up any prayer book, missal, piece of scripture or document, read it and comprehend it without any assistance. Some of them are so good that they can sit down and write in Latin without the use of dictionaries or grammar books.
I don’t think that he’s requiring priests to be able to write or converse in Latin. But he is certainly requiring them to be able to pick up the missal or the lectionary and read it fluently; that is, read it and comprehend without the aid of dictionaries or grammar books. That requires practice. I can speak to this from person experience as well. I serve in an area where Spanish and Creole are very common. After several years, I can pick up a newspaper in either language and read it fluently, meaning that I can translate it for you as I go long. This is the kid of fluency that the law requires of a priest who celebrates the EF. Again, it’s not impossible, but it takes practice.
Fraternally,
Br. JR, FFV