I think I understand your use of the words ethnic parish, but what is an ethnic personal parish?
Also, you say “the Latin church, not the Catholic Church”. Are you speaking of any Catholic Church that uses Latin in it’s Liturgy?
I’ve wondered whether the use of Latin ever really did or ever really will contribute to liturgical unity throughout the world (at least in the Roman rite). Shouldn’t this have eliminated the need for Masses said in the vernacular?
To answer the first question, I thought the term “ethnic parish” might be vague enough to convey merely a parish that happens to be overwhelmingly one ethnicity. The old ethnic parishes, though, were erected at a time when Catholics were normally obligated to be members of their geographic parish (the one within whose boundaries they lived). The exception to this would be if the bishop erected personal parishes of some sort, which would be parishes to which anyone of the specified category of persons might legitimately belong. This enabled all the Italians in the personal parish’s boundaries to opt for the Italian parish instead of the geographic parish to which they would otherwise belong. Since the obligation to belong to the geographic parish no longer applies, the distinction doesn’t mean much today, but for the purposes of studying past ethnic parishes it is important to remember that these were specially erected for a purpose.
As for the confusion over churches, there is a lot of imprecision in the way we typically speak of churches in the Catholic church, but mostly because Latin Catholics aren’t really aware of the existence of other churches
sui iuris (having their own laws). The Catholic Church is comprised of some 21 or 22 different churches (I can never remember the exact number) whose laws and liturgical norms and rites vary from church to church. So it would have been inaccurate to claim that the Catholic Church has a common liturgical language, because the Ukrainian Greek Catholic Church uses Ukrainian and Old Church Slavonic, the Maronite (Catholic) Church uses Arabic and Aramaic, etc. Another problem with our system of churches is that the Eastern Churches, as a general rule of thumb, can be grouped into rites so that one rite will be used by many churches (e.g., Greeks, Czechs, and Melkites all use the Byzantine rite), but in the West the opposite obtains so that one church uses many rites. This means that the church to which 98% of Catholics belong, which I am pretty sure is best termed the Latin church, though Roman church might be acceptable, cannot be referred to in terms of the Roman rite, since it also contains some who worship according to the Ambrosian, Mozarabic, Dominican, and other rites, as well as uses within rites such as the Anglican and Zaire uses of the Roman rite.
That’s a long way of getting around to the last question, but yes, Latin should serve to foster liturgical uniformity worldwide once the Roman rite had gained pre-eminence. More to the point, though, Latin is the cultural patrimony of every Latin Catholic, so in parish situations of linguistic diversity it
should serve as a common denominator. Obviously, the homily will need to be in a particular vernacular, but Latin is neutral territory for the rest of the Mass. The solution devised by some of switching back and forth between two (or even more) languages during Mass is envisioned as enabling everyone to understand
some of the Mass, but has the unfortunate effect not only of an aesthetically disjointed liturgy but also that potentially no person would understand
most of the Mass, something that could be accomplished if we were all as familiar with the Latin of our liturgy as the second Vatican Council mandated.