The vowel exchange "a" to "o"

[Jorge_Stolfi]

I'm just going to claim that VM is written in Zulu.

A priori it could be any language, or no language. But that means that the a priori probability of any specific language, like Zulu, Latin, or Chinese is practically zero.

To make  a Zulu proposal worth investigating, you need (a) at least one plausible origin story, or (b) evidence from the VMS. Preferably both.  The former should say why someone would have wanted to write a book like the VMS in Zulu, and how that book could have ended up taking up space uselessly on Barschius's shelf. The latter could be statistical properties of the text, similarities of (original) images with Zulu-related imagery, etc.

You have the beginning of (a), but just "the Timbuktu library could have books in Zulu" is still too vague and incomplete.

As for (b)... well, there is the pangolin   But the Zulu language has long polysyllabic words like "yintombazane" = "it is a girl".  Thus it cannot be plain Zulu with a spelling anywhere like the modern one.  It would have to be a funky spelling, or encrypted.  But then language statistics cannot provide any evidence that would make Zulu more likely than Manchu or Urdu...

All the best, --stolfi