From Longman Dictionary of Contemporary Englishtrilingualtri‧lin‧gual /ˌtraɪˈlɪŋɡwəl◂/ adjective 1 SPEAK A LANGUAGEable to speak three languages2 using three languages a trilingual medieval inscription
Examples from the Corpus
trilingual• Varro seems to have stated that in his time Massalia was trilingual, the two foreign languages being of course Latin and Celtic. 