sign language

So everybody in Maya's hometown, who haven't seen her in 20 years, still remember sign language, and not just basic words and phrases, but Kingpin who trained/raised her for the past 20 years doesn't know any?

update: finished watching the series and they actually address Kingpin not knowing sign language and I also forgot that Maya's mother was deaf so that would explain why the older relatives are still good with sign language, but not the younger cousins.