This is the 480th most frequent Dutch word.
nederlands
The Dutch language.
Here, 'Nederlands' functions as a noun referring to the Dutch language.
Hij spreekt vloeiend Nederlands.
He speaks fluent Dutch.
In this case, 'Nederlandstalig' is derived from 'Nederlands' and means 'written in or translated into Dutch'.
Mijn favoriete boeken zijn Nederlandstalig.
My favorite books are in Dutch.
Here, 'Nederlandse' is an adjective describing the language 'taal', indicating that she teaches the Dutch language.