"My friend is Australian."
Is it also acceptable to drop the 的 from the sentence and just say 我朋友 for "my friend"? Or is the 的 needed because we aren't talking about a family member?
There was a case of dropping "的“ when talking about relationship with a friend in a one of previous lessons. I bet it all depends on context how close you actually are with the friend. So it's basically a lottery and probably for the sake of not wasting time its better to just add the "的“ when friend is mentioned :D