Ask HN: What should I learn?

I am a professional with 15+ yrs experience. Unfortunately or fortunately, its not all sw dev exp. I dabbled in management, sw development, sys admin and pretty much anything that came along. I am also stuck in a very niche domain that deals with distributed systems. I know distributed systems are all the rage but I have no system sw dev experience. my sw dev exp is also very minimal.

I find myself unable to get jobs anywhere in the current tech world. I am not a hardcore developer, I have no firm grasp on any one language, I have no large scale projects as proof of my expertise. I know I am really good with programing if I were in a programing position. So I want to build some new skills and also develop a portfolio.

I find myself being pulled in different directions and keep dabbling with Ruby, Python, Go, Rust, Julia, JS and whatnot. I am a Linux guy, been using it for over 20 yrs.

I like systems dev, dist. systems, networks etc. What language should I focus on? What are some projects I can start contributing to in the dist systems space. Thank you for your time. I have C, C++ and Python experience. Most in Python, then C, then C++.