Latin was and still is the official language of the church. It has always been the tradition of the western church that Latin was the language of the mass and the sacraments. That was one of the changes that was produced by Vatican II. The council authorized the introduction of the vernacular into the liturgy. But in doing so it was specifically ordered that the use of Latin was to be preserved along with the church's rich heritage of Gregorian Chant and sacred polyphony. It would not be unfair I believe to characterize the resulting liturgical reform and the near complete abandonment of Latin as greatly exceeding the mandate of the council. That said I have no real objection to offering the Tridentine Mass in the vernacular provided a correct translation were available. Of course Roman Catholics have had for many years hand missals which translated the liturgy into English. But that actual alter missals (MISSALE ROMANUM) were always printed entirely in Latin. Oddly there are actual Tridentine Rite alter missals in English. But they are generally used by quasi and non-Catholic churches. A number of the Old Catholic Churches that follow the Mathew line use what is in some circles called the Knott Missal. This is essentially the Tridentine Rite translated into old English. Some Anglo-Catholics either use the same missal or in some cases the usage of Sarum or York. These were the pre-Reformation Catholic rites used in England. They were similar in many respects to the Roman rite but there were distinct differences as well. Following the breach between Rome and the English Church the Anglicans did away with these rites and they have subsequently become historical relics like so many of the glorious western liturgies. All of these are quite beautiful in their translations. To give you a glimpse of the rich heritage of western rite liturgical tradition I have attached some links below. There is also a wealth of information on Catholic (and some Orthodox) liturgy that can be found on the first link.
Information of the Roman and other western liturgical rites
Mozarbic Rite of Toledo Spain (in Latin)
Yes, I am aware that there are translations of the Tridentine rite: some of my prize possessions are some pre Vat II works that are in traditional liturgical English. I have an old Douay-Rheims, an old St. Joseph's Missal, and one of my most interesting possessions is a side by side Latin-English Psalter, translated from Hebrew!
One of the things that your links put me on the hunt for was a Roman breviary, and I found this on-line:
As a chanter in the Orthodox Church, the daily office is my liturgical bread and butter. I can't imagine not making use of it. While I have spent many years studying the Orthodox liturgical services, and am passably familiar with modern Western liturgics, this is the first time I've had the opportunity to browse through a Roman breviary. It has whetted my curiosity to learn more about the ancient services in the West. At first glance, it would seem to be very closely similar to the Orthodox cycle of services -- it appears that the Psalter is read through weekly in its entirety, just as in the Orthodox cycle. I knew these cycles were kept in many Roman monasteries in the past, but thought that the existence of services of the liturgical cycle (other than the mass) in parish use had died out long ago. I was surprised to find something of this detail on the web. It goes without saying that if one hopes to have these texts spiritually shape a people, they must be able to understand them. The language must be appropriate, IMHO (i.e. not the kind of thing found in the modern English NO liturgies), but the vernacular can be beautiful, understandable, correct, and transforming -- all at the same time.
You mention also Gregorian chant -- I don't think that enough emphasis is put on traditional chant forms. I, of course, am prejudiced in this regard, but I again am deeply connected with chant, and view text and chant as an organic whole, and feel that it is one of the things that most viscerally connect us to the Church of the ages. No, it will never be exactly the same as what it was like in the past -- it mutates and develops organically. We at our parish sing a Tone 1 Kievan sticheron melody just slightly differently from everyone else at this or that point, and 20 years from now, will sing it slightly differently still, I would imagine. It molds to the text, is shaped a bit by a community's "musical vernacular," and becomes a part of a living community's language of prayer.
There is of course a problem with regard to Western chant forms -- the lack of living continuity, since various polyphonic forms and musical instrumentation have largely displaced these chants, making much Western church music into a sacred art form, rather than liturgical chant. There are plenty of recordings of Gregorian and other Western chants around -- but they have the feel of antiquarianism and academic treatises all too often.
Anyway, all very fascinating, and obviously a topic close to my heart. If there is one Latin phrase that we Orthodox believe, it is the old "Lex orandi, lex credendi est."