Fortunately, John Nolan has come to our rescue to make sure we all know that Amen is Latin: " 'Amen' may be borrowed from Hebrew, but it is still a Latin word, and as such has the stress on the first syllable."
One of the problems, of many problems, with the use of Latin in the Ordinary Form of the Mass is that it doesn't make any sense to do so. It becomes an idiosyncrasy of the priest, the parish or the diocese with no real need for it other than preserving the official language of the Church by three very parochial entities.
Prior to Vatican II, the use of Latin in the Latin Rite of the Church was to unite the world's Latin Rite Catholics in a common Mass and language. No matter what Latin Rite parish you went to in the entire world, the Mass was the same. All that was needed was the hand missal for the changing parts of the Mass.
Thus an English speaking Catholic could worship in a Chinese parish and still feel as though he was in his home parish except for the difference of ethnicity. A Spanish speaker would not know what the homily was about or the announcements, but everything else would be at his fingertips in his dandy St. Joseph Missal (which I still have).
But more importantly, any missionary priest could go anywhere in the world and celebrate Mass. All he would need is an interpreter for his homily.
But now that the vernacular has splintered the Latin Rite Church, that can no longer take place, even in a single parish with multiple ethnicity and languages.
Thus if I have a mega parish with multiple Spanish, Italian, Chinese, Republic of Georgians, Russians and Jews, I would have to find priests who could speak Hebrew, and all the other languages. I could not do any of those Masses, especially the Hebrew Mass.
But if Vatican II had emphasized the importance of Latin for the unity of the Church and the sanity of priests, I could offer Mass for each language group in my parish and simply have someone interpret my homily and give the announcements. How cool would that be?