Authors who have a character who speaks another language but they have not got the basics of that language.
I read one where a Deaf ASL using American went to Paris and was learning French, which is OK, but ASL is based on French Sign Language so why didn't she seek out any LSF users who she could communicate fluently with?
You get this in TV / films too.
I watched one where the mother of a deaf boy was explaining something about his dad. She signed , "your dad wants to see you" but the sign she used for 'see' is only used in the sense of to look at someone / something, so what she actually signed was, "Your dad wants to look at you" when she meant, "your dad wants to meet you"