A science fiction book with this title was published a number of years before The Alchemist. Stranger in a Strange Land by Robert A. Heinlein was published in 1961. It tells the story of a man raised by Martians on Mars returning to Earth, where he transforms the culture.
The phrase comes from Exodus:
Moses was content to stay with the man, who gave his daughter Zipporah to Moses in marriage. And she bore him a son, and he called him Gershom, saying, "I have been a stranger in a strange land".
Gershom means "exile".