Ecclesiastical Latin was never a vernacular or street language. And I don’t know how much of the Latin Mass, either OF or EF, was actually translated from the Greek. The Creed might have been but problems did come up as you probably know.
Well, the Bible came from Greek and Hebrew translations, and parts of the Mass comes from the Bible. Also, the first Masses must have been in other than Latin, such as before Peter came to Rome (did he learn Latin?) and before Paul came to Rome (did he know Latin?). The
Divine Liturgy of St. James, an early form of the Mass, that we looked at on another thread, is almost verbatim in parts to our present day Mass, yet it was written in Syriac, a dialect of Middle Aramaic.
newadvent.org/fathers/0717.htm
Read this excerpt for the consecration:
Then the Priest holds the bread in his hand, and says:—
XXX. Having taken the bread in His holy and pure and blameless and immortal hands, lifting up His eyes to heaven, and showing it to You, His God and Father, He gave thanks, and hallowed, and broke, and gave it to us, His disciples and apostles, saying:—
The Deacons say:
For the remission of sins and life everlasting.
Then he says aloud:—
Take, eat: this is my body, broken for you, and given for remission of sins.
The People.
Amen.
Then he takes the cup, and says:—
In like manner, after supper, He took the cup, and having mixed wine and water, lifting up His eyes to heaven, and presenting it to You, His God and Father, He gave thanks, and hollowed and blessed it, and filled it with the Holy Spirit, and gave it to us His disciples, saying, Drink all of it; this is my blood of the new testament shed for you and many, and distributed for the remission of sins.
The People.
Amen.
The Priest.
This do in remembrance of me; for as often as you eat this bread, and drink this cup, you do show forth the Lord’s death, and confess His resurrection, till He come.
The Deacons say:—
We believe and confess:
The People.
We show forth Your death, O Lord, and confess Your resurrection.
The Mass did not originate in Latin.