The entropy and other statistical measures of the Voynich language is different from Indo-European languages. Zandbergen goes through this in some detail. To quote
Voynichese is nearly as information-rich as Julius Caesar's Latin, and significantly more so than the Vulgate version of Genesis.
Voynichese is less information-rich than Latin in the first two characters of each word, but compensates by greater variability in the trailer.
The statistics of Voynichese and a Mandarin text written in the Pinyin script (using a trailing numerical character to indicate tone) are very different.
There is actually a lot more of this in this and other papers. The Voynich language, for another example, has a lot more repeated words than (say) English. I seem to remember that the closest match in terms of word repetitions was with Vietnamese, and there was some speculation that it might be an invented script for that language, but that didn't pan out in detailed examination. The upshot is that it is just not realistic to just assume that Voynich is a common language written in some weird script (and, also, that these substitution games have been played before).