What's the etymology of »It's all Greek to me.« in German?

Question

When reading my Russian-German dictionary today, I came across the following German translation of It's all Greek to me:

das sind mir böhmische [spanische] Dörfer

Here are a two other variations of the above idiom from online dictionaries:

Das sind für mich böhmische Dörfer. = It's all Greek to me.

Das kommt mir spanisch vor. [ugs.] [etw. erscheint seltsam] = That's Greek to me. [coll.]

My question: What was historically so special about Bohemian or Spanish villages that made them synonymous with something inscrutable? In other words, what's the etymology of the German idiom?

Here's a passage from Wikipedia about the origins of the English phrase It's (all) Greek to me:

It may have been a direct translation of a similar phrase in Latin: "Graecum est; non legitur" ("it is Greek, [therefore] it cannot be read"). This phrase was increasingly used by monk scribes in the Middle Ages, as knowledge of the Greek alphabet and language was dwindling among those who were copying manuscripts in monastic libraries.

Answer 1

Both idioms come from historical situations in Germany.

Das kommt mir spanisch vor comes from the time around 1519 when King Karl V. (Spanish king since 1516) became German emperor. His ceremonies seamed strange to the German aristocrats and that is where regarding to this wiki article the idiom came from.

Böhmisches Dorf is from about the same time this wiki article states it was around 1526 and has to do with different parts of the Habsburgermonarchy where languages were German (in the border regions around Böhmen) vs. Czech (then also known as "böhmisch") in the core part of Böhmen, so that travellers simply did not understand names / people.