If you want some terrible headcanons,

Germany is annoyed by the fact that he practically shares his grandfather's name, in the English language.

Wales has a pet dragon.

Russia hates energy drinks. When inquired about it, he simply responds, “I’m already too powerful.” No one understands what this means.

America’s booming proclamations and Canada’s faint mumbles are due to the two having ADHD, which can impact volume awareness/control.

Germany volunteers at a local animal shelter.

Sweden builds wonderously intricate structures in Minecraft. He has grown quite famous for it on the internet, though other countries tend to tease him about it. If someone says, “Creeper Aw Man” to him one more time, he will flip his shit.

Although Austria’s most beloved artform is music, he does find some interest in painting. Due to his stubborn nature, Austria tries not to ask others for advice with it. When he does, Veneziano is the one he typically turns to.

France can make flowers bloom by winking at them.

Instead of blood, the Italy brothers have pasta sauce coursing through their veins.

The nations know about Hetalia. Some are fans, some don’t like it, and some don’t think much of it. The micronations are especially fascinated, and grateful for the recognition they receive.

England regularly educates others on magical creatures and their exploits. America listens because he thinks he's refering to the world of Harry Potter, and believes he's getting a sneak peak into a next possible book or movie.

Not only can Japan read the mood, but he can write it, as well. i.e. When someone is angry, he can make them calm.