@kitten while d/Deaf people can (mostly) read English/any written language they've learned, many consider sign language their L1 (native language), due to learning it before written language. i don't know about british sign language, but in many sign languages, sentence structures and vocabulary can be different to the local spoken/written language(s), making it easier to understand for d/Deaf people
-- at least according to my accessibility classes, i'm not deaf myself and none of the people i'm close to currently are either
