The second reason that it is important to know more than one language is that it increases cultural awareness and allows you to communicate with different people. All good methods of learning languages also entail learning about another culture, especially when your language skills get to a higher level. This awareness allows people from different nationalities and religions to get along with each other better, which is very important given the high levels of immigration. Many countries with high immigration levels have trouble with a lack of integration, and this is often because of the language barrier, so people end up being segregated, staying in communities where their own language is spoken. Even those that say they don’t care about meeting people of other cultures will have noticed these problems, and should accept the importance of learning other languages.
Finally, people should learn additional languages because it helps with their mastery of their own language and it is proven to be good for the brain. Some people believe that learning more languages leads to confusion, but besides the odd word being misused, this is simply not the case. If you learn a new language, you have to study the grammar from scratch, and therefore end up with a much more in-depth knowledge of grammar as a whole than people who only speak one language. Furthermore, if you learn languages with similar roots learning one can help you learn the others (take French, Spanish and Italian, for example).