What is the internal history of the Quenya translation of "Pater Noster", "Átaremma", published in "Vinyar Tengwar" #43? Jesus or Christianity is not explicitly mentioned anywhere in Tolkien's mythology of Middle-earth. How is it then possible that there is a translation of "Pater Noster" to Quenya? Of course, one could say that this translation has no historical siginficance in Tolkien's writings, it is not inside the invented history.
But there are another explenations. As many times stated and seen in Tolkien's mythological writings, the history he creates is the very ancient history of the world. And as all throughout the "HoMe", it seems that he never abonded the concept of an Anglo-Saxon mariner who finds _Tol Eressea_ of the departed elves, and who translates various Elvish writings into Old English:
Aelfwine. It still existed in the beginning of the 50s, and this work was done in the mid-50s. Maybe he is the one who introduced "Pater Noster" to translation in Quenya?
Yet one possibility is that a traveler from later times brought the prayer to Tol Eressea. This is supported by the fact that the translation often times approaces later English translations of the prayer more than other versions. But it may also be that Tolkien simply hadn't stopped revising the translation to that extent that it wouldn't have inconsistencies. But his time probably ran out. A situation similar to this explanation is e.g. the problem of umbrellas in "The Lord of the Rings".It may also be that the elves were introduced to Christianity by some unknown source. Peharps it was a follower of St. Augustine? This would seem possible, since Tolkien gave the elves some very Catholic like principles, e.g. monotheism, monogamy and respect for absinence.
What is then the internal history of the translation? Unless (being very improbable) any more information comes out, this is a matter of pure speculation.