noun
BAD : Some foreigner students feel homesick.
GOOD : Some foreign students feel homesick.
BAD : In my job I have to speak foreigner languages.
GOOD : In my job I have to speak foreign languages.
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Foreigner is a noun and refers to a person: 'As a foreigner who had only just arrived in England, I found the phrase 'car boot sale' very confusing.'
The adjective is foreign : 'I enjoy visiting foreign countries.' 'His wife teaches English as a foreign language.'