It's basically notes on some of the characters which he wrote to keep things straight. I don't know when they were written so some of them might not be accurate anymore but it's still fairly interesting.
There are notes for Italy, Japan, Spain, Prussia, Austria, Hungary, Switzerland, England, Sealand and America but I've only translated the Prussia and England parts
• Personality-wise, he loves to fight and often says things that will start quarrels.
• Since birth, he has been wielding his sword for his own survival, so he is very strong.
• He has gone on a rampage in Hungary and Poland before, so his relationships with these two are rather rocky.
• His manners are also quite terrible. (Prussian troops are quite known for their bad behaviour.)
• He is supposed to be around Austria's age, just a little older, but he doesn't look like it.
• He loves Friedrich II a lot. Even after his death, whenever something or someone brings up the history of Friedrich II, he'll be depressed.
• He was under Russia's control after WWII, dreaming of Italy's warm sunshine, while stuck with doing unprofitable jobs.
Initially, his hair style had not been fixed, his head was covered with his hat, and he was a pitiful character who has to endure being forced to go through tough times.
Initially, the plan was to draw him acting his age but he gradually became more childish.
A discarded character design has him with long hair and a face like Poland's.
• A self-declared gentleman but on the inside he's punkish and grunge. A rainy island country that often yearns for the bygone golden years.
• Believes strongly in the existence of ghosts and spirits. Has a strange power such that even people who do not believe and cannot see them will be able to see them once they go to England. America is the exception.
• However, he makes fun of aliens.
• On the surface, he's a cynical realist. He's quite a romanticist before he goes to sleep.
• He's quite bad at expressing himself. He himself knows that people often misunderstand him, he uses this fact for self-depreciating jokes.
• He hates France. Although their rivalry is a material for jokes, he quite admires France's culture.
• He normally acts like a gentleman but once he gets some booze in him, he becomes an unstoppable, violent punk.
• The food he produces is quite terrible but he thinks he is quite good at it. He also knows that other people complain about it.
• His hobbies and interests are cooking, handicrafts, literature, punk rock, and giving scathing criticism on America's movies.
• He could easily be the most pitiful one in this webcomic.
• His temper was quite stormy during the decades after America's independence.
Secondly, more scanlations of the official manga volume 1, pages 102 and 119 to the end.
Page 102 is a standalone bonus page
Page 119-126 is the Santa Finland story which has been shared before but I'm reposting here for the sake of completion.
Page 127-end is a Team Axis story.
Credits go to acordak for editing, cakefarts and bunniofthemoon for the QC.
[T/N: I have no idea where Himaruya got that bit about chorea being cause by stress from the Spanish rule bit. I'm also aware that the Turkey mentioned here is technically the Ottoman Empire but I'll just use Turkey for consistency's sake.]
More on chorea and the use of dancing to cure it here.