My island is loosely based on Nara (the city of polite deer) so half of my villagers are deer, but that's pretty much where the theme stops. Beyond that I have a few Japan-esque areas in my island like a streetfood alley, a Lawson convenience store, and a traditional Japanese inn. But other than that I made whatever I liked - a restaurant, a fruit forest (forest made entirely of fruit trees), a farm (which is so useful now that we have pumpkins!), a campsite, a library, a park, etc. I love the idea of themed islands and would love to visit some, but I think I would feel limited if I tried to make one myself, especially with the rather small furniture selection. Even limiting 5 of my villagers to deer-related species was hard, so I commend the people who are able to pick a theme and stick with it!