How is [x] used in medieval German?

[Battler]

"Bocks" transgressing into "pox" is a linguistic phenomenon.  Pox being used as an euphemism for Gotts is, I believe, a cultural one.

According to my research, pox, pronounced as POH, is a wrongly spelled BOH which is a Slavic word for God. P was often used instead of B, like Czeck PAN (Lord) and Bosnian BAN (a title of a ruler, Lord). PAN was also ancient Venetic god, depicted with a male goat's head, known in Greece and in Egypt. By the way, Greece in the ancient times extended at least to the present Slovenian city of Koper which was named Agida - goat town. German Steinbock as a Zodiac sign is also spelled as Steinpock in some Swabian manuscripts. There is a story in Trento region, also in Slovenian Alps, about the Steinbock with a golden horn, which was a medieval word for God who was luring the hunters to their mystical death. 
The legend about the Golden horn has its origin in Greek myths, but it was reworked in the Middle Ages, when the Zodiac sign Capricorn was named Steinbock in German and Kozorog in Slovenian. Since all these mythological creatures share the image of male goat, it can be assumed that they all relate to the ancient Venetic god Pan. 
It is possible that the medieval writers who were rewriting the ancient Greek myths brought back the ancient Venetic god Pan to allude to the Armenian (Nestorian) Apostolic Church, since the Patriarchate of Aquileia was once part of that Church, which had great influence on the Paulicians, Bogomils and Catars, as well as other pre-Protestant religious fractions.
This explanation can explain why POX was used as a swear word and why the devil was depicted as a black goat.

Even if Bog was indeed pronounced Boh in some Slovenian dialects in the early 15th century (or even earlier, if this manuscript is a copy of some earlier manuscript), no language whose speakers would have been in contact with Slovenian speakers is written using x for the h sound, at least not in the Latin script, which this clearly is. So this Pox being a poorly written Boh makes absolutely no sense.

Also, the West Slavic word Pan which means mr. or The LORD, has nothing to do with the god Pan, which, by the way, was Greek, and not Venetic. I also don't think Pan was ever depicted as a goat - that was instead the Egyptian deity of Banebdjeded, the Ram god. Then in the 19th century, occultists confused Banedbjeded, Pan, and Baphomet (originally a French misspelling of Mahomet, ie. the prophet Muhammad) to create the Satanic he-goat.

And Pox as a swear word is most likely just a minced word for Gott, similar to Bleu instead of Dieu (sacré Dieu -> sacrebleu) in French.