This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
Since 人 has two on'yomi readings, you can remember that for this word it uses じん because foreigners like to wear jeans (じん).
Tanaka’s daughter got married to a foreigner.
A drunk foreigner tried to pick a fight with me on the train.
Leg length is quite different between Japanese people and foreigners.