A translator's perspective
The scenario proposed by the site linked in the OP is linguistically unlikely:
it [the Hebrew text] may have been preserved in the Catalan dialect in Sepharad (Spain).
If 1) a Hebrew text was translated into 2) a Catalan text, and then the Catalan text was translated back into 3) a Hebrew text, texts 1 & 3 would not be identical--translation is far too interpretative a process for this to occur.
The only circumstance in which texts 1 & 3 would be highly comparable is if the translator of text 3 had an original Hebrew source to refer to as an aid to translation. But if the translator had such a source (text 1 or something close to it), translating text 2 back into Hebrew would be unnecessary.
Vallicrossa, Cassutto, Delcor, Hames, and Casanellas all suggest these Hebrew manuscripts are translations from Catalan (see pp. 68-70 here), not a preservation of an ancient Hebrew text.
One of the more telling examples, documented by Hames & Casanellas, is Matthew's quotation of Zechariah 13:7
The Biblical text reads: הַךְ אֶת הָרֹעֶה וּתְפוּצֶיןָ הַצֹאן. However, the translator has: “אני אכה הרועה ותתפזרו הצאן” which is a direct translation from the Catalan with no reference to the original. The Biblical text does not add the first person “I will smite the pastor,” but has the imperative clause “הך– smite” whereas the Catalan does have the first person “I”. However, the translator does not use the biblical terminology for the rest of the citation indicating that either he did not know it, or that he purposefully chose to follow the Catalan rather than the Hebrew original (ibid p. 78)
Since Zechariah was definitely originally composed in Hebrew, the Catalan influence on the rendering of Zechariah's words (as found in Matthew) makes it difficult to escape the conclusion that the texts of vat. ebr. 100 come from Catalan, not Hebrew originals.
If the translator of vat. ebr. 100 wanted to preserve the way the texts were originally given in Hebrew, relying on Catalan manuscripts for the Hebrew text of Zechariah would have been unnecessary and unproductive.
Appendix--Hebrew New Testament texts
At one point or another just about every New Testament text has been hypothesized by someone to have come from a Hebrew original, but the most commonly cited possibilities are the 4 Gospels and the epistle to the Hebrews. Even then, only 2 have straightforward Patristic support for the possibility of a Hebrew original:
- Matthew (according to Papias, Pantaneus, Irenaeus, Origen, Epiphanius, Eusebius, Jerome, and a variety of others. Note that Origen was a Hebrew scholar & Pantaneus claimed to have an actual copy of the text in Hebrew)
- Hebrews (Clement of Alexandria speculated it may have come originally in Hebrew but does not claim certainty).
My own work on the Synoptic Problem has led me to concur with modern scholars such as Lindsey, Tresmontant, and Carmignac, insofar as they deduce that there was a written Hebrew Gospel text, and one or more of the Greek Gospels derive from it. For a deeper dive on why I believe the Gospel of Matthew was written first, and that it was originally written in Hebrew (the Greek text being a translation), see my video series: Who When & Why - the Writing of the Gospels.
Within the aforementioned video series I argue for a Hebrew Gospel of Matthew without appealing to Shem Tob, although I do briefly mention Shem Tob Matthew in responding to objections.
It is frequently asserted but seldom argued from contemporary evidence that Hebrew was not spoken (or not spoken except in limited settings) in the first century:
- That Hebrew was a living, spoken language at the time of Jesus is discussed in my video: What languages did Jesus speak?
- For a review of the political reasons for which 19th-century German scholars tried to convince the world that Jesus did not speak Hebrew, see Baltes' work here.
For those who are uncomfortable with the possibility that Matthew might have written a Gospel in Hebrew, I respectfully suggest that it would be more effective to ask a separate question on the matter rather than arguing in the comments.