It's all too common for native speakers of English to never learn another language in their life. Most of them say things such as, "well, everyone else is learning English so why do I need to learn theirs?" While a lot of the world is learning English as it is the lingua franca right now, there are still plenty of reasons to start learning one.
1. Mutual understanding
This is a big one. As we have seen in history, a lot of problems and wars between countries typically happen because of language and cultural barriers. By knowing the language, we can understand them better and their ideas will become less foreign to you.
Before I started learning Spanish and didn't know any at all, I use to view people who spoke it as foreign and different than me. Once I was able to understand and speak it a little, I then realized that they were exactly like me just with a different way of speaking.
2. Not everyone speaks English
Yes, it's true! Not everyone you meet will speak English. According to the British Council, there are only around 750 million people that are believed to speak English as a foreign language. There is 7 billion people on Earth. That means that only around 11% of the world speaks English. Definitely not "everyone." If you want to communicate with the other 89% of the world, you might need to learn a new language or two.
3. People will respect you more
Instead of being that guy who makes everyone speak your language, or that annoying tourist saying "do you speak English?" to everyone, you will actually see that people respect you more if you speak theirs -- even if it's just an attempt at it. They like seeing that you put the effort in to actually learn and speak their language. It makes you seem more interested in their culture and interested in them. Even if it's just the basics, they will be happy that you know something.
As English speakers, we often take this for granted. A big number of English speakers don't care when foreigners try to talk to them in English, we just think it's normal and expected that they know it. Think about it from their perspective and why they would respect you more for it.
4. You will become a more interesting human being
How cool would it be to know two, five, or even twenty languages? Being able to communicate in another language automatically differentiates you from other people and instantly makes you more interesting. You will be the life of the party by knowing another language.
5. It's FUN!
Language learning can be fun, but it can also be boring. It depends on how you tackle doing it. If you do it right (and not the traditional, boring way) you will see that it can actually be very fun and rewarding.
I use to wake up in the morning everyday and instantly start learning and studying Japanese. It was so much fun to learn, but I had made it fun. If I had tried learning it the typical way, studying and memorizing, studying and memorizing, etc.. I would have been burnt out and ridiculously bored very fast.
Watch movies, read books, and listen to music in the target language. Go to chat rooms and speak with natives and other learners. Make it fun and enjoyable.
Hopefully you now understand the importance of learning a second or even multiple languages. There are of course many more reasons why such as employment, helping improve brain function, etc. but these are some of the main few in my opinion.
Why do think learning languages is worthwhile? I would love to hear your opinions!