I use Scala and Rust for libraries that need to be reliable and fast. These languages are easily interoperable with Java, C/C++ etc.

For web stuff I usually get by with a simple stack: PreactJS+TailwindCSS. I try as much as possible to use Typescript. My goal is to have lightweight sites.

For Android and iPhone apps it’s Kotlin and Swift. Interoperability allows to reuse Java and C++ libraries.

When I’m participating in a CTF I’ll often rely on Ruby, Python, or even Go, depending on what’s faster and easier to write at the moment. I know quiet a bit of Ruby but I do not really care about learning these language properly at the moment.

My games are usually made from a stack of C/C++ and Raylib or SDL. More complex stuff is made with Godot, either GDScript or C#.

I often use Haskell for simple language tools or distributed algorithms.

If I really need a solid backend, Scala or Haskell are my go to languages.

I try to write shaders for all major platforms, Nvidia, WebGL, Metal GPU etc. MoltenVK is used when no other choice.