^The use of written word is probably there just for practical purposes, a "necessary evil". Can't really be running a trade post if you have no record keeping. Just like there's that one guy at Reunion who does speak so newcomers aren't just completely lost.
Still, I do wonder how the Questir communicate some things of specificity between themselves. Like how do they say "go milk the Dzo" in a way that is not mixed with "go fetch water" or "go kill a mammoth" or something. If they start using any sign language with discernible words in it, that's a problem too, right?