I know that learning a language, you can simply buy a book, follow the examples, and whenever possible try the exercises. But what I'm really looking is how to master the language once you've learned it.

Now I know that experience is one major factor, but what about learning the internals of the language, what is the underlying structure, etc.

There are articles out there saying read this book, read that book, make this game and that game. But to me this doesn't mean to master a language. I want to be able to read other people's code and understand it, no matter how hard that is. To understand when to use a function and when another, etc etc.

The list could go on and on but I believe I've made the point. :)

And finally, take whatever language as an example if needed, though best would be if C was taken as an example.