This is the 5754th most frequent Catalan word.
foreign
The Catalan word for "foreign" is "estranger" (adjective). Definition: Belonging to or originating from a different country or nation.
In this sentence, 'estranger' ('foreign') is used as an adjective to describe the nationality of the director.
La pel·lícula que vam veure era d'un director estranger.
The movie we saw was by a foreign director.
Here, 'estrangera' conveys the idea of something originating from countries other than the speaker's own, modifying 'literatura' ('literature').
Vaig estudiar literatura estrangera a la universitat.
I studied foreign literature at the university.
In this example, 'estrangeres' is an adjective describing customs ('costums') that originate from a different cultural or national context.