Culture doesn't limit anything. Toilets are always the place for ghosts. Living creatures "mark" their territory simply by smell, this is the same. Us human breaths out an air called "Yang Chi", which is basically telling the ghosts that "This place is mine" and keep them away. This is why ghosts don't haunt crowded places. There are some exception of course, but mostly crowded places aren't where ghosts want to be. Toilets, storerooms, abandoned houses on the other hand, the best places for them. So even if your school's toilet didn't have any bad history, it can still be haunted by ghosts.
This is a fact: Earth has a history of 4.5 billion years, and human has been on earth for at least 10000 years that had a decent "culture". How many people died? Countless, everywhere. There are no place on earth that doesn't have at least 2 corpses laying underground. So, ghosts are everywhere. But like I said, we don't see them because there are "rules". We have something keep us from them, and they're less likely to stay in my room where I sit on my chair 20/24. Where else should they stay? Toilet, we only come there now and then, some extreme household doesn't use the toilet for weeks. Perfect place, no?
Hanako-san is just a rumor about a ghost in the toilet, it doesn't mean only Japan has it. Heck, my elementary school had one too, the door was locked from inside and we heard sobbing, but when we took a peep through the gap below the door, there was nobody. The the toilet flushed and we screamed, running away.
I had been through 5 schools in my life and remembered quite a lot of "things", but nowhere had a "7 mysteries", because we're not in Japan lol.