The 'Chinese' Theory: For and Against

[rikforto]

However, the same texts can be spoken out loud in any of them without changing the written words. [...] They can see the exact same texts and just pronounce them as they like locally. (and within the proper Chinese dynasty regions as well, the dialects are as varied in the past and maybe even more)

This convenience even extended to ancient Japanese, Korean, and surrounding regions influenced by Chinese culture.

But Japanese and Korean are not monosyllabic, so they don't seem to match the morphology of Voynichese words.  Unless the local medical/astrological/pharmaceutical language was not really Japanese or Korean, but mostly some bastardized Chinese-like language...

It was perfectly ordinary for someone to learn the vernacular readings of the Chinese characters, but be fluent in writing Literary Chinese. The vernacular readings extended to places that adopted the characters---Japan, Vietnam, Manchuria, Vietnam, etc. The neat trick here is that you can write it down with one pronunciation and it is completely and totally legible to someone who has never even heard of your language so long as they have some way of reading Literary Chinese. (A longstanding problem was that this wreaked havoc on poetry, but those details aren't worth getting into until they are.) I'm going to illustrate this with The Romance of the Three Kingdoms, which was written by a Chinese speaker, but I am going to recover the readings in modern Korean. I'm just going to do the first five characters, to keep it brief.
話說天下大,
화열천하대,
hwa yeol cheon ha dae,

I want to stress, this would be a very common and natural thing for a Korean scholar in, say, 1420 to do---at least if you account for the 600 years of Korean sound changes I cannot be bothered to look up. Our scholar would not only understand this to be Chinese, but it does not make any sense as Korean; it is monosyllabic and it does not have inflections or the needed particles to make it grammatically Korean. He could also write a letter to Luo Guanzhong thinking in these readings, and Luo would not have any major clues that they did not share a system of reading the characters and be able to continue the correspondence readily. "Chinese with Korean phonology" (or Vietnamese or Japanese or Jurchen or...) would not be very surprising---well, after the shock of finding literary Chinese in a European manuscript!