Cultural appropriation is a sensitive topic. People react to it much like they react to the word "privilege": they feel accused, they feel guilty, and ask what they're expected to do about it.
Sure enough, the answer is also "nothing special, just be aware of it".
How exactly? Let's look at some typical examples from fantasy fiction:
Ghouls are a Middle Eastern myth. Maybe don't use them out of context, okay?
Banshees are an Irish myth. Maybe don't use them as discount ghosts, alright?
Wendigos are from Native American myth. Not just an exotic local boogeyman.
Yes, it's alright to write stories about people and cultures not like you. And in fact I can think of a very famous British writer who managed to turn even European myths into racist caricatures. Even some myths from her own country. But that's just it. We can do better, right?
I've seen it said on Tumblr that it's okay to use samurai and ninja however we like because have you seen how Catholic nuns are portrayed in manga and anime?
Yo. You wish real Catholic nuns were half as cool. That's the difference.
More recently, I keep seeing strigoi from Romanian folklore featured in World of Darkness-style stories. I don't mind at all. Can't speak for other Romanians. But I beg you to do some reading about them first, because in some ways they're way cooler than the average modern vampire. So is the real Vlad the Impaler.
Nobody thinks you're a villain. And I love to see how other people see me. Just be aware of what you're doing, please.