Persuade me on my next language. Right now I use python. Debating between JavaScript, Go, or C/C++. You'll get a ++bomb prize for responses that are detailed and include good resources for learning. Commence!

Reason...because I want it to become the standard way of coding React apps and every recruit helps...

All of the above.

They all have their purpose and use cases, and as a developer / programmer you should not be restrained to a language but to a greater level of knowledge to use many languages to solve your problems where appropriate.

Learn C++ because you can write python modules with it.

I recommend boost python. It has nice api.

Rust or Go or Scala.

Given your profile, you might want to go with c++ purely because you code on Windows. But you could code everything else as well.
I recommend Go to everyone simply because it has a low learning curve with high value being added to performance and practices via Go strucslts&interfaces

And you can use web assembly with c++ and you have web development

Alright, seems like C++ and Go are out in front. No explicit calls for javascript - not too surprising lol.