Tolstoy once wrote with every language you learn, you gain a new soul.
Being multilingual does not make people stupider than they are, indeed, some may improve. I have been raised with three languages (Turkish, Swedish and German) from my early childhood on. And some imperfect school English and daily IT pidgin additionally.
It’s not the obvious fact that you speak several languages acquired by childhood, education or training, but you have much more behavioral facettes and cultural skills. You are more likely to adapt and understand different perspectives and different types of people in your professional and private life. Because of each language will treat your thinking differently. Perfect for communicational skills, cognitive phenomena of mental perception and insight. Perfect for entrepreneurs and consultants.
Here are two different links you should read if you are interested:
- The Benefits of Bilingualism. (The New York Times)
- In German: Wie die Sprache das Denken formt. (Spektrum.de)
BTW, it’s not important which different languages you speek for this reason. Tamil, Yoruba, Polish, Sardu and Cantonese Chinese or Finnish will do too. And it does not matter if you speak your second or third language perfectly or not. I do not speak any of them as I should. No worries. Just do your conversations. People will understand.