Hope you are enjoying problems at AtCoder. Here, I would like to discuss one topic ignored for a long time.
When you create an account at AtCoder, you must select your country for your profile. There are, of course, a bunch of options as there are many countries, including the countries Japanese government officially doesn't recognize (Palestine & Taiwan), and even Cook Islands and Hong Kong.
Meanwhile, there is one (UN member) country you cannot select on AtCoder: Democratic People's Republic of Korea, a.k.a. North Korea.
As a competitive programmer, you might come up with recent achievement of a North Korean team at World Finals this year. They won silver medals. Still, they cannot compete in AtCoder contest unless they wear another country on the profile.
Did they just forget to add the country? It is highly unlikely. I have found that issue years ago, and I have asked about the issue time to time. The only reply I got to the clarification (at a test round) "It seems impossible to select North Korea at the profile settings." was, "Yes."
So, why don't they want to add the country to the list? Because it's time-consuming? I doubt it takes more than minutes to add one country to the list. Because the government might feel uncomfortable to have many accesses from North Korea? There are tens of thousands of people living in Japan who have North Korean nationality as well (because of historical reasons). Because there were some North Korean contestants at Codeforces who surely cheated and they want to avoid cheaters by banning all the residents from one country? Well, that would be no different from racist groups. (Plus they wouldn't ban China just because of ScarletFirebolt or Saudi Arabia just because of the cheater hacking ksun48's account.)
AtCoder isn't "AtCoder 2012" where the problem statement is provided only in Japanese anymore. Isn't "AtCoder 2019" providing the chances to everyone over the world to solve interesting problems? The officials, please understand that "internationalization" means not inviting only top-tier coders to make the contest look better, but inviting every coder without discrimination.
I'll repeat the final paragraph in Japanese as well:
今の AtCoder は日本語だけで問題文を提供して日本人にコンテストを提供する「2012年のAtCoder」ではなく、世界中の参加者に面白い問題を解いてもらう「2019年のAtCoder」だと信じています。運営のみなさん、「国際化」というのは上位の強い人を招待してコンテストの名声を高めるという意味ではなく、どの国であっても差別なくコンテストに参加できるようにすることではないのでしょうか。