Had to look it up. Britranica says:
The Stranger, enigmatic first novel by Albert Camus, published in French as L'Étranger in 1942. It was published as The Outsider in England and as The Stranger in the United States.
Which explains it i think. Translate suggests foreigner too.
I think i prefer "Stranger" or "Foreigner" - "Outsider" does too much of the novel's work i think, like if Irvine Welsh had called his debut novel "Heroin addiction".
Anyway I'm rambling. The reason i asked was i didn't know it was also called The Stranger and that makes more sense of one of the nihilistic angsty anthems of my early youth, Killing an Arab, by the Cure, where the lyric is "I'm the stranger"