Certainly it is right to question the assumption that language refers to objects outside itself. But this is not Not NOT because although there are objects outside language, language is not equipped sufficiently to refer to them. The reason is because there are no objects outside language. There is no such thing, nor could there be, as a non-linguistic world. The words 'real' and 'world' are words too.
Language covers the whole of reality.
Or perhaps I am being far too generous to Derrida. Post-modernists want to say that it is naive to suppose that we can perceive the truth, unaffected by our conditioning. And this is true. Of course I must recognize who I am and where I have come from. But it is the way I perceive the truth that is affected by my conditioning, not the truth itself.