I am firmly convinced that it is not a hoax, ancient to modern.  Besides that, I have only some theories, but not much faith in any one.

I see no reason to believe that the text is unrelated to the illustrations.  So it is probably what it seems to be: a compendium of herbal, medical, and astrological stuff.  Unfortunately, only a couple of plants can be identified with certainty, and they grow all over the world.

In my view, the statistics of the text fit either: (a) some East asian language with monosyllabic words -- like Chinese, Tibetan, Vietnamese, Burmese, Thai, and several others -- encoded in an invented alphabetic script, possibly under dictation by someone who did not understand what he was writing.  Or (b) a codebook cipher, where words of the dictionary are mapped to random numbers and these are written in some invented system similar to Roman numerals.

In either hypothesis (a) or (b) I don't have much hope of deciphering it.  If (a) is true, to decipher it one must identify the language (among hundred possibilities), learn it with the vocabulary, syntax, and pronunciation of 500 years ago (and we know that Chinese changed a lot in that time), figure out the orthography that the author used (which can be very complicated because of tones) and then wrestle with the inevitable scribal errors (it is quite possible that the book we have is just a copy of an older original, made by someone who could not read it). If (b) is true codebook ciphers are notoriously hard to crack.