Because I already know C#, and why waste time learning Java which is very similar; what would I gain?

I chose Go over C++, because it looks easier.

What do you gain from learning Go?

Obscene speed and learning a language built with concurrency in mind.

Go's goroutines are superior to threads in C#.

C++ is harder and there's no garbage collection.

I now have to yet again close my apps and restart my computer for an IT-forced Java runtime update, for some app I rarely use. For that reason alone I'd not consider Java.

From what I can tell Go's goroutines are pretty similar to C#'s await functionality.

But I don't want you to use C#/C++/Java, I want you to use Nimrod.

I forgot that C# added more asynchronous stuff since I last coded in it. I used to love C# but it's more verbose than Go and I'm weary of the obfuscated MS documentation that pushes me straight to blogs. Also I gave up on using Windows for web development.

This is the first I've heard of Nimrod.

Plus there is rx reactive, tpl and tpl dataflow.

If I'm not mistaken, that's a fallacious slippery-slope argument. I'm still undecided on how to weigh language popularity against other factors, but surely relative popularity is an important factor in things that have a big effect on real-world software development, such as availability of libraries and tools. For now, at least, Go is much more popular than Nimrod, and also has more people working on the language implementation and surrounding tools.