Being 22 years old I can't imagine living without the knowledge of any foreign language at all. When I was younger I thought that knowing different languages is important; now, I think it is necessary. Today, the world is like a one global village: people communicate all over the world, they make international friends and travel easily. In today's world not knowing another language is like being a mute being not able to express the most basic needs.
Let's take the example of English language. Almost all world is learning English...so should the Americans and the British resign from learning foreign languages? Of course not..
Firstly, not all people speak English. I will give you an example from my own life. Two years ago I took part in IST project during my studies. I visited a small village in France where we (the group of Poles, Czechs, Brits and one German girl) met a lady (she was our host) who came from Switzerland. She knew French, German and English, but she refused to speak the last one. There was a funny situation when she listened to the conversation in which the British also took part (the conversation was in English) and answered their questions or expressed her opinions in French or German. The British seemed quite astonished... they were forced to use foreign language and they did it.
Secondly, knowing another language is " good for your brain". You practice your memory and your communicative competence is higher. When speaking English I somehow feel that my mind works...and I am sure that it also works with other languages!
I regret that I know only one language well.. I've been learning German for five years but I don't feel good at it.
I can't imagine myself not knowing English at all. This will deprive me of the opportunity of travelling, experiencing the world and making friends...