Yeah, I think their definition of mastering a language is pretty low. I live and work a lot in French and have for a while. While I would consider myself fluent I don’t think I’ve mastered it. I make guesses about vocabulary and grammar all the time and when people ask me a grammar question about French grammar I often don’t know the answer. I usually have a vague feeling that what they are asking about is either wrong or right, but can rarely tell if that is because I have developed some sort of intuition about the language or because I have just developed my own bad habits. Practice makes permanent, after all, not perfect.
TL:DR. The more fluent I get in French the more I realize I will never really master it.
