This might not be among the top few worst arguments I've ever seen, but it is one of the oddest... meaning not only do I not agree that it's valid, but I also can't imagine how anybody would think it was. With a lot of other bad arguments, I can at least see how/why they succeed in tricking some people.
In this case, the basic structure seems to be X→Y→Z, or "X is true, which implies that Y is true, which implies that Z is true". X is that the Old Testament was written in the language & alphabet of enemies of its target audience, and Z is that the mythology in the Old Testament is false, but Y is missing; we're given no way to get from the thing about languages & alphabets to the thing about the reality or unreality of anything supernatural or even the historical accuracy of a historical document's historical claims.
By itself, the missing middle step is a fairly ordinary kind of argument failure, AKA the "Underpants Gnomes Fallacy". But this case has another twist: not only is the first step (X) itself already false, but the OP makes it perfectly clear that he
already knows that, because his only attempt at a defense of the claim is actually a debunking of it. Without going digging for the original exact quotes, it went like this:
►Leumas: It was written in Canaanite, the language of their enemy
►Somebody else: It was written in Hebrew
►Leumas: Hebrew is a Canaanite language/dialect
...Well, yes, that's true; Hebrew is in the Canaanite language family. (There is no individual language called "Canaanite" within that group; it's just the group name.) But that means "Canaanite" isn't the foreign language of the Hebrews' foreign enemy; it's a family including their own language. The only possible basis for a claim that an old Hebrew book was written in "Canaanite" is the fact that it was written in Hebrew and Hebrew is a Canaanite language, which inherently debunks the claim that the fact that it was written in "Canaanite" means it was written in some non-Hebrew language. It's like looking at a book in Danish, describing it as being written in a Germanic language because Danish is a Germanic language, and then trying to use the fact that the book was written in a Germanic language to somehow mean that it wasn't written in Danish, when the fact that it was written in Danish was the only basis for saying it was written in a Germanic language in the first place.
So, in our X→Y→Z argument here, we not only don't have Y, but we don't even have X either.
But that wasn't all; Leumas's realization that Hebrew is a Canaanite language also means that (s)he knew that a pseudoanalogy (s)he used along the way was wildly false too: the thing about America's founding documents not being written in any of the native languages of North America... where the native languages were unrelated to English. What in the world could that possibly have to do with a separate invasion story in a different time & place in which the invaders' language was in the same language family as those of the invadees‽... which we already know Leumas knew because (s)he used that as the only basis on which to say that the invaders' books were written in a member of the invadees' language family!
But wait, there's more! None of the above even mentioned the strange obsession with the alphabet being the "Aramaic alphabet"... which is the Hebrew alphabet in a only slightly different font. The main thing it's notable for compared to other historical alphabets is how little it has changed, really no change at all for most letters. We modern people looking back just call it two different names in two different contexts, but that isn't how people in that area looked at it back then. It was just the alphabet... just like our alphabet is, to us, just the alphabet; they wouldn't think of the Aramaeans while using it any more than we think of the Romans while writing English. And what's with the obsession over the fact that it's an abjad, and where are "flowed/flawed" and "incomplete" coming from? I guess that all must be about alphabets without dedicated letters for vowels being somehow inferior, but the languages that have been using such alphabets for thousands of years are a demonstration that it works fine for those languages. (They even have ways to mark vowels with diacritics these days, but people normally don't find that even worth bothering with.) And the bizarre praise for the Greek alphabet as the better one for Hebrew-speakers to use was especially absurd. That alphabet started out as functionally the same alphabet as the Aramaic one (different-looking but really just versions of the same 22 letters for the same 22 sounds), but needed so much modification for Greek that it wouldn't be suitable for a Canaanite language again without a similar amount of modifications back in the opposite direction!
I've seen some weird linguistic nonsense before, but this is like somebody set out to try to see how bad (s)he could get with surreally weird linguistic nonsense on purpose. This stuff is to linguistics what that Star Trek TNG episode with characters turning into ancestral animal forms was to evolution.
... however... you are still making the same mistake... that being not reading the stuff properly.... I suggest you read them again and carefully and see how nowhere do they say that the Bible is a lie. 
