Children pick up languages very quickly, and if they grow up bilingual, it makes it easier for them to learn others as well later in life. That said, Klingon would be one of the more useless languages to be multilingual in.
I am not sure the bi-lingual hypothesis has been demonstrated to be true. I can think of several people who know 2, 3 or even 4 languages but as adults have not been able to extend understanding to a 5th or 6th language.