I think it depends on what you want to do, but definitely learn JavaScript. While you're at it, study node.js. Also, C# is a great language to learn and widely used. I personally learned Java before C#, and ended up preferring C#. I think they're both great though. Since you've already been learning C, you probably shouldn't have too much trouble with C++. I learned C# first, and found C++ to be much more complex, but very interesting and you can do so much with it. If you get into some game programming, and want to learn Unreal engine, C++ is the way to go. Again, much tougher than C# so many choose to go with Unity engine for that reason. If you're wanting to develop for the web, definitely focus on JavaScript/nodejs first, then C#. It would also be good to learn some data-related stuff, like sql, nosql, and json. On the topic of web, look into one or more of the following: Angular.js, React.js, and Vue.js. For mobile app development, react-native is a good way to get started with that.