I'd like to know what your two cents are on this. Let me preface this by saying that as far as my career is involved, I'm really open to anything although game development and software development are on a pedestal.
The only language I know right now is C++, and I plan on sticking with only C++ for a few more months (for data structures and some more OOP, as well as reading Effective C++ and Effective Modern C++). In this time I also plan on learning about Qt, and was eager to dab around with Unreal Engine as well. After this, I'm not really sure what is recommended to learn.
Some people have told me that no other languages really complement C++ like, say, Java or Python. It makes sense to learn more languages, but I just don't know what approach to take for picking up my next set. I was looking at something like this as it covers most of the paradigms.
Also, what should I be learning about outside of languages? I have command line and git on the list but other than that, I'm not too sure what I should be geared toward.
There is no "after C++" you will be trying to master it for the rest of your life... ;0)
What you learn next depends heavily on what you want to do.
what should I be learning about outside of languages?
Networking and communication protocols, the cloud and IoT spring to mind.
Real-time/embedded/mobile development, always good to learn how to do things efficiently.
Parsing techniques.
Secure programming.
Data Analysis.
AI/Machine learning.
Well, after I got C++ kinda under my belt, I've moved onto Java. The nice thing about C++ is that it is a low-level language. When I went from C++ to Java I was like, whoa! Java does a lot of the nitty gritty stuff for you! But Java is pretty different (but similar) in comparison to C++. Or, if you want to do something easy, HTML, CSS, and JavaScript are good too. But those are web-based languages.