Should you Learn more than one language?
I will say this, if you are coming from university, it benefits you to stick with one language as your go-to. It'll make tech interviews more comfortable and deciding on courses easier. When it comes to working for a Fortune 500 company, they don't care what languages you know. They expect you to be able to pick up any language within a couple weeks and at least be able to use it on a basic level. But, that being said, while you're in college, you should explore other languages in your free time / summers. Just learning OOP and standard libraries in most languages gives you a good idea of how they work.
Learning how to build a web app might teach you things about computers and networks in general. But it's not a good idea to make that your main focus. I think you should focus strongly on one language and take it as far as possible.
It comes down to learning something very well. Bruce lee said it best "I'm not afraid of the man who has practiced 10,000 different kicks. I'm afraid of the man who has practiced 1 kick 10,000 times". Be great at something, don't be "just okay" at many things.
However, on the other hand, if you work for a Big 4 company and only have to code in Java. If you only studied Java and C++. You can do your interviews in C++. But it will be expected of you to code in Java. Your job will expect him to know the finite details of Java because his code needs to be 100% performance.
This of course is just one example. But it is important for you to start