The Rohonc Codex is an undeciphered manuscript that was kept in the city of Rohonc in Western Hungary (now Reichnitz, Austria), until 1838. The paper on which the codex was written bears a watermark that identifies it as having originated in Venice in the 1530s. Generally it is supposed to be in Hungarian, Romanian, or else a hoax.
First, I think there is no question at all that the content of the codex is biblical. Consider the following image:
This depicts the scene described in Matthew 21, where Jesus rides an ass into Jerusalem, and the people spread their garments in the way, and cut the branches from trees and spread them in the way.
But obviously this is not written in a (known) traditional liturgical language of a Christian tradition, nor is it written in a (known) vulgar language of a Christian population. I think it is very possible that it was intended as a secret text, either because the Christian sect was considered heretical, or else because the practice of the Christian religion was circumscribed.
One of the interesting things about the imagery of the codex is how the Romans are depicted. Here, you can see them crucifying Christ:
The Romans appear to have tall, pointed caps with something like a tassel on it. I believe this text was composed within the domain of the Ottoman empire, and the author was depicting the Romans as Janissaries. You can see what I mean in this picture of a Janissary:
The text uses a double-dash as a hyphen at the ends of a line to indicate breaks in words. Interestingly, these hyphens normally occur on the left side of each page, demonstrating that the direction of the text was from right to left, perhaps influenced by Arabic or Hebrew writing. This usage of the hyphen came into being with moveable type, and so we should consider primarily areas of the Ottoman empire that were in the European sphere.
So, let's say this text originated within the Ottoman empire, somewhere not too far from the general trajectory between Venice and Reichnitz. At the time the paper was manufactured, the empire included most of the Balkan peninsula (including Albania). Hungary, Transylvania, Wallachia and Moldova were quickly added. Theoretically, the language could have been Hungarian, Romanian, Serbian, or even Macedonian or Albanian.
It's getting late, and I'm tired, so I'll just throw one more thing out there.
Check out this page of the text (which reads right-to-left). It has what appears to be a numbered list, wherein the numbers are prefixed with a curly-V looking shape, followed by a repeated formula:
The symbols for the smaller numbers are just slashes. The first element on this page is number 4, so there are four slahes, then five slashes, then the number six is represented by a semicircle with an angle in it, then seven is that plus a slash, eight is that plus two slashes, nine is a bent t, ten is a cross +, eleven is a slash with a dot, like a lower-case i.
Suppose the curly-V represents an ordinal prefix, so these entries read something like "Fourth, it sayeth in XYZ...", "Fifth, it sayeth in XYZ...", and so forth. If that's the case, we should focus on languages where the ordinals are indicated by a prefix.
In Romanian and Albanian, the ordinals are prefixed by the definite article. Romanian is closer to Reichnitz, but my money is tentatively on Albanian, because several scripts were invented for Albanian in the 18th century, including one (the Todhri script) that used many of the symbols used here for numbers.