interlanguage vs lingua franca

interlanguage and lingua franca both are nouns.

Word	Noun	Adjective	Verb	Adverb
interlanguage	Yes	No	No	No
lingua franca	Yes	No	No	No

As nouns, interlanguage and lingua franca are synonyms defined as:

interlanguage and lingua franca: a common language used by speakers of different languages

Other synonyms of interlanguage include koine.

interlanguage (noun)	lingua franca (noun)
a common language used by speakers of different languages	a common language used by speakers of different languages