The order of the Mass is taken right out of the order of the synagogue service. This is easy to see even if one attends a modern synagogue. The language of the consecration is taken directly from the prayers used at the Passover.
What makes you think that Justin’s account is “loose”? It is clearly the same order of the Liturgy that is used all over the world, both East and West.
There is no evidence of formal daily prayer gatherings in synagogues at the very least into the second century and maybe into the third, and there is sketchy evidence of what form these prayers took at this time.
The Eucharist is modeled after the meal prayers in the home. Justin’s description is loose because he basically leaves it up to the presider to pray extemporaneously.
"and we always keep together; and for all things wherewith we are supplied, we bless the Maker of all through His Son Jesus Christ, and through the Holy Ghost. And on the day called Sunday, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons. "
While there may be a pattern there is no set Church order of prayer (as in set texts) for the celebration of the Eucharist. Even the Didache does not give specific prayers but simply gives a description of a Eucharistic and an Agape meal. The Eucharistic prayers come from the Berekah prayers at meals, but were probably not formally set. This was fused with a synagogue style “liturgy of the word” once the ancient Christians were forced out of the synagogues.
The point of all this is that no where in early texts describing the Eucharistic celebration does it say it was said in Latin until we get to the use of it in North Africa around the 4th century.