How accurate is the depiction of 13th-century Poland in the Conrad Stargard series?

by Zalachenko

Leo Frankowski's Conrad Stargard books depict an engineer from late Soviet-era Poland transported to 13th-century Poland ten years before the Mongols invade. In that time he has to make a name for himself and industrialize his country to save it from the hordes.

From what I recall, Frankowski—himself a mechanical engineer—does his homework when it comes to adapting modern technology to a medieval setting, laying out in explicit detail how Conrad uses his limited resources to create rudimentary aircraft and radios. But I'm more curious about his credentials as a historian. In particular:

Sex is treated with surprising candidness in Frankowski's medieval Poland—nudity taboos are relaxed or nonexistent in many villages, for example. Conrad sets up a Playboy bunny club (the Pink Dragon Inn) but gets the Catholic Church's approval because it's "look-but-don't touch" and the women's virtue (that is, virginity) is intact. Frankowski does use the right of prima nocta as a plot point, so I take his worldbuilding with a grain of salt.
Conrad is able to communicate with his 13th-century countrymen because modern-day Polish, according to him, is relatively unchanged from its medieval incarnation. He relates an anecdote in which he tells his friends how drastically English changes with time and geography, and they think he's telling an ethnic joke.
Conrad's close confidante, a Franciscan monk named Ignacy Sierpinski, is commissioned by the Church to report on Conrad's status as an instrument of either God or the Devil. Through a cocktail of bureaucracy and slow communication, a letter of Ignacy's bounces through various channels to the abbot of the Franciscan monastery in Cracow, by which time Ignacy himself holds that position. He answers his own letter again when it's forwarded to the Bishop of Cracow shortly after his elevation to that office.

In short, how did popular views on sexuality in 13th-century Poland differ from Church teachings? How stable is the Polish language over seven centuries? And given the limitations of long-distance communication, could an ecclesiastical official potentially be promoted to the very office he wrote to before the letter reached it?

Sex: Not my area of specialty, but virtue in the middle ages went far beyond virginity. While public nudity was quite likely far less of a taboo than in the 18th-19th century, especially among peasants, actual stripping could be seen as just another form of "selling one's body", and could fall into "carnal desires". There were, after all, groups forbidding dances because you could touch a woman.

As for the promotion, it is a fairly amusing plot device, but there were matters taking years in medieval Europe. Of course it's highly unlikely that someone like an actual time traveller with almost supernatural knowledge would not be personally invited to Krakow to meet the Bishop or the local lord/abbot. (It's also somewhat unlikely for a Franciscan, a friar that made vows of poverty, to become a Bishop of Cracow, about as powerful as a duke).

As for the language it's absolute poppycock. Here's the first recorded Polish sentence, coincidentaly coming from the same period:

Daj, ać ja pobruszę a ty poczywaj

In modern Polish it would be:

Niech ja pomielę, a ty odpoczywaj

Indeed, there was a relative period of stability in the language, but it happened roughly 400 years later, after invention of the printing press. Old Polish from around 12th century was significantly different than the modern form, with its grammatical oddities now surviving only in dialects or proverbs, for instance it used the "dual number" apart from singular and plural.

In short, had our time traveller found himself in, say, 1580, he might have a chance to be understood and understand others, as if a modern Pole from Warsaw found himself in, say, an isolated Lithuanian village inhabited by a Polish minority. In 1400, maybe it's a bit like Polish and Slovak, related, but not intelligible. And in 1200s, he would still be talking a West Slavic language, and certain concepts could be understood. He could probably say he wants food and water - but saying "I think we should open a strip club" would be rather impossible.