bilingual

adj. fluent in two languages, expressed in two different languages, in two different languages

n. one who speaks two languages fluently, bilingual speaker

The term multilingualism can refer to an occurrence regarding an individual speaker who uses two or more languages, a community of speakers where two or more languages are used, or between speakers of different languages. Multilingual speakers outnumber monolingual speakers in the world's population (de Bot & Kroll).
See more at Wikipedia.org...

Noun
1. a person who speaks two languages fluently
(hypernym) linguist, polyglot
Adjective
1. using or knowing two languages; "bilingual education"
(similar) multilingual

adv. bilingually, in a bilingual manner

adj. bilingual, fluent in two languages, expressed in two different languages

(a.)
Containing, or consisting of, two languages; expressed in two languages; as, a bilingual inscription; a bilingual dictionary.