It highly depends on what you're interested in.
If you want to learn Windows desktop application development, you should look into C#.
If you are interested in web development, you should learn HTML, CSS, JavaScript, Angular.
If you're interested in creating games, you should look into C++ and learn a game engine like Unreal Engine. Or learn C# with Unity game engine.
If you're interested in embedded programming, microcontrollers, then C, C++ and even Assembly are the relevant tools you'd need.
I'd also advise "mastering" one object-oriented language first as the same principles, design decisions, design patterns, etc most of the time can be carried over to other object-oriented languages.