People sometimes used to say that exist must be ambiguous because look at the difference between 'chairs exist' and 'numbers exist'. A familiar reply goes: the difference between the existence of chairs and the existence of numbers seems, on reflection, strikingly like the difference between numbers and chairs. Since you have the latter to explain the former, you don't also need 'exist' to be polysemic.
"Let us forget once and for all the very idea of some knowledge of language or meaning that is not knowledge of the world itself."
What must be given up is a picture of language in which the characters at the level of sentences are generated by some underlying referential mechanisms at the level of words. This “bottom-up” picture is misguided because the references of words depend upon the characters of sentences.