Learning backend developing and how to learn as experienced developer
I've been working with PHP for several years now (probably over 7 years) and I would say that I'm an experienced web and PHP developer. During the years I have also looked into other programming languages like C# or Java from time to time, but without really having a goal in mind.
Now I would like to learn something new and this time with a goal in mind. I would very much like to develop bots, hacks and servers (game servers or web servers).
My question to you guys is: Which programming language do you think would be the most suitable for this? What do you think is a lot of fun and could I also like?
My other question is: How do you learn a new programming language as an already experienced developer? After all, I already know how to work out solutions and solve problems and I would say that I have a solid basic knowledge of the theoretical aspects of computer science and programming. So how can I, as an experienced developer, learn a new programming language fully but effectively at the same time?