Reposting my comments:
It's not any "medieval Poland", it's another world altogether with people and creatures from different worlds and most have Germanic and/or Celtic names. The 'true' protagonist Ciri (Greek name) in the books repeatedly visits ours world (Earth) in various places and eras, and I don't think it's Poland even there (unless the German owned Prussia counts), instead she goes to France and so on. It ends with her in King Arthur's Camelot (in the aptly titled last book, The Lady of the Lake).
Now, Sapkowski himself often commented on how little of his inspirations were anything Polish or generally Slavic. It's mostly Western and Northern European. When he began writing about other things, he wrote about King Arthur (again) and about the medieval Czechia (The Hussite Trilogy). His themes are quite extremely non-Polish for a Polish author, because most Polish authors do write about Poland, and also most Polish authors are completely unknown elsewhere for this very reason as Poland is such a globally niche and unappealing subject, while he doesn't.
How many other Polish fantasy (sci fi, alternate history) authors did you as much as hear about? Yeah, probably none, and that's precisely because usually they really write about Poland, and so practically no one outside Poland cares about it. (Maybe you heard about Lem, who didn't.) Sapkowski's Witcher books are internationally successful because they're not Polish but just European, using Arthuriana plus assorted various mythologies / legends and continental history (one particularly big theme is Rome vs Celts), and Tolkien's modern fantasy (and, yes, Moorecock).
Some people take it to the other extreme, like I've just read on twitter in response to an ignorant "Polish legends" a challenge of "okay, name just 2 Polish legends in The Witcher". This went unanswered (because almost no one outside Poland knows about any Polish legends), but actually I would "name just 2": strzyga & skrzaty. But both of these are not really Polish but wider Slavic, and more importantly they're just among the massively greater myth and legend body in the books that isn't Slavic at all, but from elsewhere in Europe.
Yes, but that's not what I talk about here.
What I mean it's a distinctively European fantasy but also virtually non-Polish besides just the country of origin.
In the books there are only vague mentions of exotic other lands that are never visited - they could have made a Netflix spinoff about a pseudo-North Africa / Arabia (Zerrikania, separated from "Europe" by an almost impassable desert) if they cared about staying true to the world as in the source material while trying to diversify their adaptations. They could well cast Arabs for such a spinoff. Maybe even Africans, or whatever Sapkowski would tell them they're like because actually it's not really clear (like 2 Zerrikanian girl warriors appear in the books, but an early comics adaptation made them white or Asian as far as I remember).
Elves are also all white, and even more importantly didn't even come Earth (unlike the humans who came from Earth). But Netflix made them multiracial humans with just funky ears. They look, talk, and behave just like humans and their culture is exactly like human even before they ever met any human. Amazing.
I really wonder what made it downvoted. A mention of Zerrikania? In the games you can see a Zerrikanian person, he's very much a darkie there.
(He's also only one, because these lands are very much separated just as I mentioned.)
In the books, Zerrikanians may also well be white too: https://www.reddit.com/r/witcher/comments/9e3dh2/psa_a_misconception_about_zerrikanians/ (Maybe so, and the twins in the comics actually weren't white. It's been over 20 years and I don't remember.)
But also as the post mentions, there's also even more exotic Zangwebar (a pseudo-Africa named after Zanzibar).
They are internationally successful, because of the video games.
Look at the publishing dates of the English translation. There's a large year long gap between the first two (one short stories and blood of elves) books and the rest. I think it's something like 5 years? The book franchise was dead for the English market - you don't wait 5 years for the 2nd book of a series to translate.
The translations started again after Witcher 2 was released.
Apart from that I agree with you. Sapkowski draws inspiration from many European folklore imho especially British/Arthurian/Celtic/Irish. Lady of the Lake (Nimue), Geralt's death, Wild Hunt (Unseelie Court), Tir na Lia (see Tir na nog), Muircetach (see this guy).
I'm curiously being downvoted why you're being upvoted while you say you agree with me.
Well, the book series (short stories in the Nowa Fantastyka zine at first) had become popular in Poland in first place because it wasn't actually Polish but just mainstream (international style Tolkienian) fantasy with a few instances of what we call "smaczki" and which may losely translate as easter eggs (not quite but I don't really know how to translate it).
Very Polish fantasy lit is more or less niche even in Poland, and even Sapkowski's own later Hussite series wasn't even remotely as successful despite or rather because being set in Slavic lands with Slavic characters (it's a historical fantasy), and I only know it exists because nobody talks about it.
While Witcher was always an instant hit in Poland, with multiple adaptations in various media in the first decade alone (there was even a Polish TV series, and the original video game adaptation project of an Alone in the Dark style game with set cameras) because it was a Tolkienish English fantasy (Moorecock), reworked to be explicitly Arthurian, with only some Polish-like "smaczki" for to feel just enough "swojsko" but not too much.
Without this early succeess, there would be no games.
This is somewhat debatable as greater Slavic lore is the basis for a large portion of European lore, but Slavic lore can also be traced back to ancient Greek and Egyptian ties as well.
Yes, it's to some degree overlapping, but then there's the matter of naming. For example, as noted in https://twitter.com/Dataracer117/status/1607649036269649920 that I just saw, the elves are traditionally Germanic creatures (and got popularized in modern fantasy by Tolkien, along with dwarves and orcs) and in the Witcher they have Irish names and Irish connections. (Nothing "Polish" about them too, just like with almost everything else.)
You’re overlapping polish over Slavic. Slavic lore is probably the most normalized in most fantasy and even Christian literature. The modern depiction of the devil is actually based on the Slavic depiction, same as when you think of witches, etc. this is mainly due to the geographic location of the Slavic region where it was the central hub to have numerous influences such as Ancient Greek, Egypt, Khazaria, Franconians, etc.
And also there's for example a Polish version of the basilisk legend (bazyliszek), and actually more than one version, but no one's going to say how basilisk is a "Polish" creature.
Actual-Polish legends are stories like Sir Twardowski (Pan Twardowski), a hard drinking noble wizard having bizarre adventures like going to the Moon with the Devil or what not (if you think of Terry Gilliam's film The Adventures of Baron Munchausen you're spot on), or the old legend of the evil king Popiel who was eaten by mice in his tower after being cursed for reasons (I don't remember). Nothing very appealing to the global audience.
It's also the case of most local European legends and entire mythologies, very few are even remotely as appealing as Greek, Arthurian, or Viking. For example even a relatively popular Irish being there only to a degree.
And a big reason is neither the Romans nor Greeks ever reached Poland, so they didn't record anything and there was nothing written before the Christianization in 966 after which still almost nothing was written about the local culture for a long time (and the Germans, having civilized themselves after cannibalizing Rome, earlier evidently didn't find it interesting too).
The Glagolitic language which is the precursor to Cyrillic was the first written language of the Slavs and developed by the Greek orthodoxy. Rome was the creator of the word sclavus and the Byzantine sklabos which means Slavic, and is the root word for every Latin based languages word for slave. Again you are putting polish before Slavic when is should be reversed, it is akin to saying Frankonian over Germanic
We talk about Poland now. Eastern Romans had a plenty of contact with the Slavs (for example some Ukrainian cities began as Greek colonies), but never reached Poland (literal backwoods, just like the Baltic areas). Obviously we also never used Cyrillic.
The first person to actually write about Poland (even generally speaking as in a territory) was a Jewish slave trader probably doubling as a spy for the Islamic Iberians, in the late 10th century (Ibrahim ibn Yakub).
Polish/Slavic mythology witches (wiedźmy) traditionally were pretty much just hags in the huts in deep woods. That's how they appear in the disntinctively Polish/Slavic legends I know. Prominently, Baba Yaga (Baba Jaga).
I think sorceresses (very negative czarownice) is a foreign import, as is enchantresses (much more positive czarodziejki). Via Germany at first (along with limited witch hunts - polowania na czarownice, Hexenjagden), and the French culture as it became the culture of Warsaw (the countryside nobility was instead into an Oriental-like bizarre "Sarmatian" culture influenced by the Ottoman Empire: https://culture.pl/en/article/the-elegant-downfall-of-the-polish-sarmatians).
The enchantress/ sorceress was Ancient Greek and recycled first through Roman mythologies then later adapted by Germany
There are various archetypes of magic-women all over the world, the Polish original was a weird old woman living alone in the woods. I don't think we even had pagan priestesses.
Evidently we had goddesses with supernatural powers (usual for deities), as with Marzanna relegated to a czarownica in a quasi-Christian folk ritual. She was possibly a Slavicized Hecate.
Baba Yaga is Slavic unique and originally was penned in Russian Cyrillic, every modern depiction of a witch is based of the Slavic Baba Yaga. The broom, cauldron, hut, boils etc. the pointy hat is just a transference of the original horn.
The cauldron motif is Celtic. The wiedźmy used just pots.
I believe the pointy hat thing in at least it's iconic form (with a belt buckle on it) is modern English if not just American (their Salem incident obsession involving a Puritan colony).
Other than that I don't even know what I'm supposed to be arguing about here.
Also now I think the game's skrzaty were created as pixies for the main international (English) version and it's just a translation to Polish as skrzaty, as there's no Polish version of the word pixie at all. Skrzaty (aka krasnale/krasnoludki) are different creatures, like the German gnomes.
Actually there's even no Polish word for a fairy (fae/faery) whatsoever. All that exists is "wróżka" for the fairy godmothers in, well, fairy tales (in the meaning of modern German and Danish fables), an absolutely ridicalous choice of word because wróżka means a female fortune teller.
(There are actual versions of fairies in most of all other Slavic languages, usually simply phonetical writings in local alphabets. But Poland's instead super awkward as so often.)
Your argument is flawed in the idea that Polish culture must only come from Poland. I've had to explain to my wife that many of my beloved German or Argentine traditions are from other cultures. Heck it's a joke that Argentines get homesick when they see pictures of Italy.
Sapkowski uses many motifs just unknown in Poland until very recently. For example for his noted Arthurian obsession, it is known that there was another big fan in what is today Poland (due to her having Lancelot-Grail frescos in her tower) in the 14th century or so, but besides that singular instance with no cultural legacy Arthuriad only really arrived in Poland by the way of the American and British late 20th-century pop culture going global. The core of The Witcher is Arthurian Romance + Tolkien + Moorecock.
I'm not going to argue on polish history and culture because you will win. However, there are a lot of things that seem old and are new in every culture. Santa Claus in the US really didn't kick in till the 50's. Ireland didn't really celebrate St Patrick's day until the late 90's.
Claiming something is from another culture therefore not the culture doesn't work.
Arthuriana was introduced in Poland in the 1980s-1990s during the SF/fantasy boom and the fascination of the Western culture that wasn't suppressed anymore (for example during Stalinism one could be even jailed for things like being found listening to jazz and the beatniks were literally enemies of the people, while in the 1980s it was trendy among the youth to be completely openly and outwardly members of metal or punk subcultures without much consequences, with Polish and bands holding concerts legally). Just to remind you it was so completely foreign until just few years before Sapkowski began writing. (Maybe besides some knowledge of Wagnerian treatments, but Wagner slso wasn't halal for the hardcore Communists due to how much the Nazis enjoyed his stuff.)
Now, it's like to say "it's now also Japanese culture" (King Arthur is hugely popular there nowadays, not just Fate and stuff but also scholarship), making people say the actually explicitly Arthurian Witcher is thus set in "medieval Japan".
(And the Polish Witcher TV series actually did give Geralt a katana, which was often ridiculed at the time by the Polish fans, similar to how the retards at Netflix now gave a katana to their Chinese Elf.)
King Arthur is absolutely not the Polish (non-pop) culture. There were medieval Arthurian (Tristanian) works written in Czechia and Belarus (Ruthenia), but in Poland there were only some books imported from France or Germany if which none even survived. Just like "stories featuring Avalon and Camelot" is certainly not what you think if you hear the phrase "Japanese culture".
Geralt's katana sillyness: https://images.kinorium.com/movie/shot/239237/w1500_48798595.jpg
Look up Captain Kronos Vampire Hunter. It was a 1970's hammer horror film.
Are the monsters from Polish folktales at least? That's what I thought people referred to mostly
Almost none.
Here's some lists: https://www.reddit.com/r/witcher/comments/3vq1uf/witcher_monsters_books_vs_games/
Out of all of them I can only point out to drowner (topielec), besides striga (strzyga), and with both of these being Slavic in general.
Oh, and leshy and kikimora (both also generally Slavic, too). That's 4.
Dragons if you really want to push it, being global (due to dinosaurs).
A few like ghouls aren't even European.
And actually just checked, and the skrzaty appear only in the games (in Blood and Wine) where they're translated in English as pixies (and wearing leprechaun hats). So, uh, wouldn't "name 2 Polish legends in the books" out of top of my head, too.