foreigner vs stranger

foreigner and stranger both are nouns.

Word	Noun	Adjective	Verb	Adverb
foreigner	Yes	No	No	No
stranger	Yes	No	No	No

As nouns, stranger is a hypernym of foreigner; that is, stranger is a word with a broader meaning than foreigner:

foreigner: someone who is excluded from or is not a member of a group
stranger: anyone who does not belong in the environment in which they are found

Other hypernyms of foreigner include alien, unknown.

foreigner (noun)	stranger (noun)
a person who comes from a foreign country; someone who does not owe allegiance to your country	anyone who does not belong in the environment in which they are found
someone who is excluded from or is not a member of a group	an individual that one is not acquainted with