Q. I don't know why anyone would think that the Mass should not be in English! Don't we see, in the New Testament, Jesus giving His disciples the gift of tongues to be able to spread the Good News to the nations in their own separate languages? Didn't the Holy Spirit come down on the Apostles so that the people could hear them in their own languages? Isn't this exactly what the English Mass is doing today? I'm glad Vatican 2 saw that a new Pentecost was needed with vernacular Masses leading the way!
First, Vatican 2 didn't change the language of the Mass from Latin to the various national languages. In fact, Vatican 2 called for "the use of the Latin language is to be preserved in the Latin rites." (SC, 36). The Council did allow for some use of the various modern languages, but the idea that Vatican 2 wanted (or even foresaw) Latin being entirely abandoned in the Mass is as wrong as it is oft repeated.
Second, the gift of tongues signals the exact reverse of putting the Mass into various languages. The descent of the Holy Spirit at Pentecost was reversing the punishment God laid on mankind at the Tower of Babel. Before Babel all men spoke one language, every could understand everyone. After the pride of man was raised by sin to such a fever pitch that man tried to build a tower to Heaven, God, ending this ill-conceived project, confused men's languages. The various tongues that man would come to speak ever after is a divine punishment. The Spirit, at Pentecost, reverses this when the apostles are able to preach and be understood by all (just like all men could pre-Babel).
Taking the Mass from one universal language, a language that all Catholics share in common and that privileges no group inside the Church, and putting it into a multitude of ever changing languages has made our worship more like Babel and less like Pentecost. It divides us from our ancestors (who worshipped in Latin) and from other nations (who worship in other national languages). Before the Council, a Catholic could travel and hear Mass in Latin anywhere in the world. No matter how strange the rest of the customs of a foreign land might have been, the Mass was the same - the same language, the same movements by the priest, etc. This was a visible expression of the universal ("catholic") nature of the Church. Today, with the nearly exclusive use of all vernacular Masses, each nation has its own translation of the Mass, its own version of the Bible for the lectionary, etc. Travel now to a foreign country and the Mass is as foreign as anything less you run into. You will find the same structure and be able to follow along, but gone is the homey familiarity of stepping into a Church and being surrounded by the entirely familiar.
In fact, you don't even have to travel to another country to experience the division that can occur when we worship exclusively in modern languages. Where I live even local parishes are divided by the language used at Mass. We have English Masses, Spanish Masses, Chinese Masses, Vietnamese Masses, etc. We've gone from a Pentecost-like environment where we can all worship together in one common tongue, where all can understand, to a Babel-like state of rupture and division.
Further, by losing Latin, we've lost the patrimony of sacred (not just religious, but sacred) music. Masses by Palestrina, Mozart, Beethoven, etc are all lost and replaced by Matt Maher songs (not that I don't like Matt Maher, but his music isn't sacred nor is it Palestrina, as even he'd admit.)
Switching to an almost exclusive use of the vernacular might make the Mass immediately more understandable, but peasants (with less than a middle school education) were able to understand the Mass for centuries despite it being in Latin. Catholics today, especially here in the West, are more educated than Catholics have been at any time in the past. In this day, when we find ourselves more and more isolated from our past and from other cultures, perhaps a return to Latin would be a salve for the soul.