Why and how the text could be Bavarian

[dashstofsk]

a hybrid cipher-language system ...  encrypted with something like a disk/wheel

It would be too burdensome to have to pause the writing after every word in order to consult some code table or spin a disk. It would drive anyone potty.

And also why the strange alphabet? It just adds to the trouble. Encryption could have been made simply with the local language, with no need for an invented script. Also was it really necessary for every word in the manuscript to be encoded, and that none of it could be written in the local language? Even the one word labels of the celestial objects? Did the meaning of every single word have to be hidden from a third party? ~225 pages and ~36000 words all had to be laboriously encoded?

I think you are thinking too hard about the manuscript. The solution is probably more simple.