How perfect is Voynichese?

[ololololo]

Yes, but not always. It depends on what substitution we apply. In the case of VMS, for example, knowing the language won't help us much.

Why so?

Well, I can assume that it's written in Latin, because that's the most obvious option for a medieval book. I won't get anything from this assumption, as I don't know how it's encrypted.
At the moment, the assumption about the original language of the manuscript is unprovable and does not provide us with much information.
It would be possible to compare some words and try to identify the substitution, but you have already read my thread and seen my attempts to do so. Of course, there is some similarity between the words, but it is impossible to extract anything from it.