Back in the day, I took part in Ukrainian, and then German math olympiads. If you're interested, have a look at the webpage of my ''home team'' in Lower Saxony. Every year, the organisers are looking for volunteers to grade the students' papers at the Landesrunde in February. Also, if you're in the mood for some olympic problems (with solutions and sorted by strategy), I can recommend this book.
I'm a fan of languages, linguistics, and fun etymologies, and I enjoy translating and interpreting. During my Master's I had a student job in Roland Meyer's group, doing some basic statistics for corpus linguistics and learning about digitalisation of manuscripts.
In August 2018, together with my friend Manuel Radons we organised a very intense 3 week course at Deutsche SchĂĽlerakademie about random graphs and programming for a group of gifted 17-18-year olds. Here you can see the course announcement (by looking up our names). It was fun! In the last week, Manuel went crazy and offered a spontaneous crash course in Galois theory.
Another reading recommendation: The AMS article "Voices from the Bombed Universities of Ukraine" features interviews with Ukrainian mathematicians.