I've remained with the impression that, while Qestir tradition dictates silence, on certain occasions both written and spoken words are used as a "necessary evil", albeit as sparingly as possible. For example, teaching spoken and written language to very young children, so they can deal with outsiders. That's why Qestir are able to understand us so well. Also when they are extremely agitated and frustrated with an outsider they may drop a word to make themselves clear. There is a Qestir in the "Who Needs Words" quest whose text reads: "Khaishan is so worried he is on the verge of saying something".