Or why there are bathrooms with no window, even on an external wall...
If you are having a bath, or shower, you would rather not want anybody watch you :)
2. No, there are two much older. Neither is Iceland's. One still (and always) legally in force.
If you mean the American one, they have written that the 3rd May constitution was the first in Europe, the second in the world (after just the American one). If you know an older one - tell us about it :)
Something that isn't known even by most of Poles is that between 1974 and 1991 Poland had the tallest object in the world - a longwave radio broadcasting antenna. And nothing tallest had been built anywhere before 2010.
When he emigrated there wasn't even a Poland on the map.
And what does it have in common with his nationality? Poland didn't exist on the world map for 123 years, but it survived as a nation, although the occupying countries were doing their best to destroy Polish culture. I wouldn't say it's anything unique, but still the lack of Poland on the maps doesn't mean he couldn't be a Pole.
According to Wikipedia he was Jewish. But there were many Jews that considered themselves Poles at the same time. To be sure about his nationality, one would have to find sources relating what he was saying about it.
Considering the fact about dog names - personally, I don't know anybody having a dog called Burek. It's known as an example of a name for a dog (another, maybe even a more popular one, is Azor), but I don't believe that there are such statistics at all. There is, however, a proverb "Nie jednemu psu Burek" - literally "Not only one dog is called Burek". Meaning is rather obvious.
About secondary education - currently the final exams (Matura) are deliberately made simple to make Poland look well in statistics.
About Kevin Home Alone and Christmas - I wouldn't call it a tradition, but actually there were some protests of viewers when a TV station that had been showing this movie every Chritmas for a long time (Polsat) once decided not to do it :)
About the film dubbing - it refers only to TV, not to cinemas, and this way of translating movies isn't called dubbing :) It's better than dubbing in that you can still hear the original actors. Dubbing in Poland also exists, but on TV it's used only for movies for children, or for some "for the whole family". In cinemas the films are usually displayed in two versions - with dubbing and with subtitles. Subtitles aren't used on Polish TV almost at all. If so, then rather as an addition to a Polish soundtrack, for the deaf people (they aren't normally displayed on the screen, they are sent via teletext on the 777 page, or now, in the era of digital TV, via the "DVB subtitles").