Ask HN: What does it mean to learn a new programming language?

When I pick a new language to learn, I can pickup the basic types, control, syntax etc. in a few hours and write basic programs while referencing the language docs/tutorials. I can also write few mid sized programs while learning about the standard library in a few days of learning a language. But often times the programs written aren't the most efficient in terms of the programming language. One example is learning c after working with a grabage collected language like python tend to not use pointers and instead make multiple copies of the same data i.e not use one of the better features of the language. So does the programmer know C?