why the voynich ist celtic

[Jorge_Stolfi]

We don't know who created the VMs or where they came from. We don't know where the VMs was created. What we can sometimes discern from the illustrations are the influences and experiences that the VMs artist considered significant enough to represent in the manuscript and how that information has been manipulated.

I would say a bit more.  We can be quite certain that the Scribe -- the person who actually put quill to parchment -- was "substantially European" and experienced with writing "European" documents on parchment, in some "European" language other than Voynichese, using Latin letters.  That is, his/her experience was not (solely) writing in Greek, Armenian, Georgian, Cyrillic, Arabic, or Hebrew.   

And it also seems safe to assume that he/she had some "European" herbal and astrological manuscripts available for "inspiration" when drawing the images. 

On the other hand, there is evidence that the Scribe knew the Voynichese alphabet
but did not understand a single y of the text.  So much so that he would write a parag that was supposed to be a single column with a plant in the middle as two columns, offset by one line...

All the best, --jorge