It depends on what you'll do.
I do mobile app development (apps that you see on your phone) and my primary language is Java and Objective C.
Personally, I think it's relatively easy to switch between languages, so learn a few very well and you can usually pick up new ones.
For example, I think C# and Java are very similar. Objective C is weird and different, but learn a few patterns and you'll get used to it.
The tech sphere changes rapidly, so don't count on your "best" language to be the one you will use at work. I hear stories of .NET engineers not being able to find relevant careers (https://blog.expensify.com/2011/03/25/ceo-friday-why-we-dont-hire-net-programmers/).
By the way, I've personally never used C++ at work. I learned it a little bit at school.
I've talked to engineers at other companies who use Go primarily. I haven't learned Go, but it's a pretty new exciting language.
Be versatile and be willing to learn, and you'll have no problem!