How do you know that you've reached expert level at some programming language?
When you stop reading and start answering questions in Stack Overflow. When you start consulting the official manual of the language to check for difficult to interpret programming details. When you contribute to the community When your co-workers use you as a reference for the language When you start seeing beauty (and ugliness) in programs When you start disliking the code you did some time ago, because now you know more than that When your errors become much more complex, because you don´t make simple errors anymore When even without thinking your code is consistent, and you follow the same programming patterns and they are all clearly good.