Actually the Gospel of Matthew and a few others were not written in Greek at first. We can also check against the Diatesseron which was used as the Gospel text of Aramaic speakers for @ 200+ years, which was made by adding the Gospel of John to an already existing harmony of the other three Gospels quoted by Justin Martyr.
First of all, I don't understand why in reproducing my six-month-old comment, you supersized the font instead of simply reproducing it as typed. There is, after all, nothing controversial in the quoted sentence. The collection of texts that the Catholic Church refers to as the New Testament exists solely in an old form of the Greek language. Any and all testamental source material, whether actual or hypothesized, is distinct from the Church's sanctioned texts, just as any subsequent versions of the collection or of its individual texts are, strictly speaking,
translations of the NT, not the NT itself.
______________________________________
With regard to your comment quoted above, there are several things to say. Apropos the first sentence, I am unaware of any scholarly source that postulates a non-Greek original or primitive form for any Gospel except Matthew. Put the other way around, every account I have ever read states plainly and decisively that Mark, Luke, and John were written in Greek from the outset.
Furthermore, while the existence of an Aramaic original of Matthew is something that is universally agreed upon, no fragment of it has existed from time out of mind. What is more, the presumptive Aramaic original was what has been called proto-Matthew, a first draft of the Gospel later extensively revised (probably twice revised) before it reached the definitive form given canonical status by the Church in the latter part of the fourth century, a status that was dogmatically confirmed at Trent in the face of the Protestant challenge. In short, any relevance that proto-Matthew has is a text-critical matter, not a doctrinal one.
As for the Diatesseron, cited in the quoted second sentence, I do not see its utility to the present discussion. First of all, it was composed no earlier than 170 AD or so. Second, there is no basis for thinking that among the Gospel materials it contains in digest form are any texts that antedate the canonical Gospels. Nor is it even established whether the Diatesseron was originally drafted in Syriac or originally drafted in Greek and then translated into Syriac.
All in all, the need filled in its day by the Diatesseron was catechetical, not doctrinal or historical. That specific catechetical need no longer exists, and whatever historical significance remains does not shed any light on either the docuмentary or kerygmatic sources of the New Testament.