Interchangeable ch/sh and k/t characters

[MarcoP]

We are dealing with words that differ by only one consonant, such as, for example, in French the words "bateau" (boat), "château" (castle), "gâteau" (cake), and "râteau" (rake). 
Do they all mean the same thing?
And what about the verbs: "disait" (was saying), "gisait" (laying), "lisait" (was reading), "misait" (was betting), "visait" (was aiming)?

That’s an interesting parallel and a great opportunity to remember how peculiar Voynichese is. First, character entropy tells us that Voynichese isn’t a phonetic rendering of a European language: we know that Voynichese glyphs do not behave like vowels and/or consonants in French, English, German, Latin, Greek, Italian etc.

Second, while in ordinary European languages it is possible that an initial character can be replaced with a different initial, this is much rarer than in Voynichese (where the phenomenon is systematic). In You are not allowed to view links. Register or Login to view., I only find 190 couples that differ by only the first character, while I find 1004 for the top 1500 Voynichese words.
For instance, daiin has these variants among the top 1500 word types:
daiin 850 / saiin 127
daiin 850 / kaiin 79
daiin 850 / raiin 64
daiin 850 / taiin 45
daiin 850 / oaiin 25
daiin 850 / laiin 14
daiin 850 / paiin 7
daiin 850 / yaiin 5

Third, word frequencies for matching pairs in French often differ by a whole order of magnitude.
E.g. t/b matches:
ton 15513 / bon 11483
tout 47221 / bout 4571
tete 11999 / bete 1706

This of course makes sense, since the words in a couple typically are semantically unrelated and the match is "coincidental". This also happens for most of the 'daiin' examples above, but it usually doesn't happen for ch/sh.

Also, in most cases the t/b replacement doesn’t work in French:
trouver 16833 brouver?
temps 16785 bemps?
toujours 14336 boujours?
…

Compare with the top ten Voynichese ch/sh matches:
chedy 507 / shedy 434
chol 395 / shol 185
chey 352 / shey 278
chor 211 / shor 95
cheey 185 / sheey 149
cheol 173 / sheol 108
chy 164 / shy 98
chdy 146 / shdy 45
chckhy 140 / shckhy 60
cheor 93 / sheor 47

Here the replacement almost always works and typically results in comparable frequencies (max/min < 3).

EDIT: as always, it's possible that I made errors, but the differences with European natural languages are so huge that I think you can get the idea in any case.