Well, as unaccustomed as I am to defending the Latins, as a matter of fact, there are portions of their Mass which are in Greek and prior to the promulgation of the Latin Mass centuries ago, the Liturgies in Rome were chanted in Greek. In fact, they were nearly the same in form as ours are today. In the early Church at Rome, the language was Greek. The Roman Church learned its most basic theology in Greek, mm. Latin, Rome's theological language, isn't Greek, nor is it Slavonic, but it does come a close third when it comes to a theological language. In fact, though, Greek is the liturgical language of a number of particular churches whose hierarchs are in communion with the Pope of Rome.
"Are you saying that they are NOT The Church, then?"
Not at all. The Church of Rome is very much a part of The Church. The fullness of The Church is found in every single Roman Church diocese, just as it is in my Orthodox metropolis.
"Is the Orthodox one the only true one since it understands and prays in Greek?"
I don't know if Holy Orthodoxy is the "only true one" praying in Greek or not. These matters are up to God. That said, we do pray,
"We have seen the true light; we have received the heavenly Spirit; we have found the true faith, worshiping the undivided Trinity, for the Trinity has saved us."
but we pray this because we believe we do have the True Faith. We don't know everywhere it can be found, though we generally can say where it is not found. Forming a theology based on very bad translations of Scriptures probably will lead to one of those situations where the True Faith is not found, at least not in anything approaching its fullness.
You mean like the Catholic Bible which deliberately mistranslates passages like Genesis 3:15 where the translators replaced the personal pronoun *he* in the Hebrew to *she* to support their idolatrous doctrines of Mary?
Or perhaps 2 Corinthians 7:10 where the Catholic Bible mistranslates the word "metanoian" as *penance* instead of the correct *repentance*?
You need to be telling this to the Catholic contingent. They're the ones who dismiss the importance of Scripture to begin with in favor of tradition and then work with the translation of a translation. (Greek to Latin to English).
What do you consider *true faith* and how do you determine if you have it?
This is a very important thing for our Protestant friends to grasp. The Church is a hierarchy of hierarchies, and each local Episcopacy models the Church Catholic. Further, each local parish models, with some necessary alterations, the Episcopacy, and each house forms the Church Domestic where the man of the house is also the priest of the house.
Each time the question is raised, "why wouldn't the Pope just order X", that is the answer. The bishops are sovereign princes of their dioceses. We are held together by faith kept in common, not by command and control structures.
St. Peter spoke of "living stones built up, a spiritual house, a holy priesthood, to offer up spiritual sacrifices" for a reason.