DotNet is closest to Java, but hang on to your hat: the state of C# is at least half a decade ahead of Java, if not a full decade. It’s sophistication will make Java use feel like banging rocks together. DotNet Core can now run on all three primary platforms, and with some careful work, you can write a single program that can compile down to each platform and carry along its own required binaries, no pre-install of any framework needed.

My second recommendation would be Rust. Stupidly steep learning curve, but an absolutely game-changing one where safety and security is concerned. It’s my next objective, personally speaking.

Any other language I could recommend starts getting into speciality purposes, which makes general use more difficult or even wholly inappropriate.

For example, if you are dropping into DotNet for business applications, I would also recommend diving into F# for that functional goodness for building complex business rules and data handling. But building an entire app in F# can be jamming a round peg into a square hole under many circumstances, it’s appropriateness envelope does not cover as many cases as C# does. You want to use C# for boilerplate/frameworks, F# for the core bits where it is going to shine.