This is the 5259th most frequent German word.
australian
The German word "australian" does not exist; the correct term for "Australian" in German is "Australier" (noun) or "australisch" (adjective).
Here, 'australian' is used as an adjective to describe the origin of the movie.
Ich habe gestern einen australischen Film gesehen.
I watched an Australian movie yesterday.
In this instance, 'australian' functions as an adjective to describe the nationality of the students.
Die australischen Schüler lernen auch Deutsch in ihrer Schule.
The Australian students also learn German in their school.
Here, 'Australien' is used as a noun to denote the location or geographical region.