What are the key areas do we consider to justifiably say someone is a competent English speaker?

Listening

Speaking

Reading

Writing 

Well, I always tell my students that it's not simply speaking but rather communicating ideas. All elements of the language work together to present a meaningful statement. The syntax, the lexicon, the rhetoric, and the grammar should all be beautifully and explicitly molded together to make that statement. However, since simplicity is beauty, we can still express ourselves elegantly with the minimum words possible as long as we know what we are saying.