I love the Harry Potter series, and I truly admire the care Rowling put in developing her magical world. I guess that's why I feel so increadibly cheated ever since she claimed that Durmstrang would be in northern Sweden. This is why that is stupid.
All the known characters from Durmstrang seems to be Eastern European. No Scandinavian names at all, and the clothes definitely don't seem Swedish or Norwegian in the very least.
I recall Rowling guessed that Durmstrang would be in northern Sweden, but any description including "mountains" pretty much eliminates Sweden as an option. Norway is more likely, but it still seem like poor research on Rowling's side.
If the school is situated in... Norweden? What kind of language would they speak? Concidering that the headmaster (Karkaroff) is... Finnish-Russian? (seriously, what's up with that name) and they accept students from Bulgaria. The logical conclusion would be to teach in English, but apparently magic negates logic to such degrees that they've had to do something else... Or maybe Krum is an idiot and don't talk at school and thus never got around to learning good English.
The Scandinavian wizards all go to pubic school, probably in Denmark on some small unplottable island, or get home-schooled. Except the muggleborns would have to be home-schooled in someone else's home, but regardless I doubt they would be left hanging. If nothing else it would be dangerous to have a bunch of magically capable but untrained muggles on the loose, randomly setting off magic.