its strange that epiphanius would think it was in Hebrew, he was roman and anti Jewish. not likely he would make it up.
it also makes no sense for the Essenes, who wrere deeply connected to Christianity, whote in Hebrew just like the other Jewish sects. and the early Jewish Christians, we are told, would deviate from this. why the change? they wanted to be more roman?
Irenaeus and Epiphanius, referring to Papias, spread the legend of the Hebrew original of the gospel of St. Matthew. But from Papias report it is not entirely clear whether it is really about the Hebrew original of the same Gospel that we know as "Matthew."
After all, the canonical Matthew has a very close literary connection with the text of Mark, Matthew gives many quotations exactly according to the greek Septuagint, by all signs the canonical Gospel of Matthew was written in Greek and among his main sources was greek text of Mark.
As for Papias' account of Matthew, who "wrote Jesus' sayings in Hebrew", most likely we can talk about some early collection of the logias of Jesus, like the Gospel of Thomas, and it is quite possible that such a document was attributed to Matthew in the time of Papias.
By the way, regarding the Gospel of Thomas - it is very suitable for many signs of Papias' description of the document "Matthew". Moreover, modern researchers come to the conclusion that the original language of the Gospel of Thomas was precisely the Syriac.
When we comparing the Greek fragments of the Gospel of Thomas with his Coptic text, the existence of different versions of this document is revealed in the early period of it tradition, and the version preserved in the Coptic translation appeared, apparently, as a result re-composing of logias (if we assume that the Greek fragments correspond to an earlier version of this document).
In the early period many documents only began to "seek" their "authors": thus, the synoptic gospels until the second half of the second century were nameless (they were called memorable writtings of the apostles, or each gospel was simply called - "Gospel") and only by the time of Irenaeus began to be called "according to Mark", "according to Matthew", etc.
The same can be true for the history of the emergence of the name of the Gospel of Thomas. In the time of Papias document like the Gospel of Thomas (some of its early edition, as discussed above) can be issued as writting of Matthew. Papias could perceive the Syriac language (= Aramaic dialect) of this document that it is the Hebrew language. So could have appeared the legend of Papias about Matthew, that he wrote in Hebrew. This document could be attributed later to Thomas, with the strengthening in Syria of the cult of this apostle.
My opinion is that Papias reports an early document that was known at that time as the writting of Matthew, this document was subsequently revised and in later distributed as the Gospel of Thomas (ie, Papias tells not of the canonical Gospel according to Matthew).