I think not just Americans but everybody should have some type of experience with a second language. The world is to big and too culturally diverse to just adhere to one language, we are built to connect to each other. Language is everything, is translates culture and understanding. Not only that but it does help you out in your career if you speak more than more language. There is also a handful of benefits associated with learning a new language including higher general intelligence.
The reason I say that is because language is always evolving. Even the English language. It's not the same as it was 10 or 20 years ago. People use slang and other mixed words.
Translations aren't always correct. Do you think that internet will be around forever? Of course not. With the technology evolving. Who know? We might need to learn a new language just to use it. The second widely spoke after English is Mandarin Chinese. People prefer not to speak English. I mean you don't have to learn second language but it will really come in helpful.
It's not necessary but it will become a useful skill if you go on business trips around the world. Being able to talk the language vs. Having a translator is worlds different from each other. Being able to directly talk the language will allow you to truly engage with the other as people and read mannerisms and really connect with the person.
This is America, our first language is English, we don't need to learn another language. Most of the teacher in different countries are now teaching students English. We don't plan traveling out of the states, and if we do we can always hire a translator to help us understand and communicate with others.
1. Learning a new language (assuming your first is English) will only open the door to speak with a few other people in your neighborhood in normal cases.
2. We have this nifty new thing called a computer. It can translate things.
3. Lots of work for a little reward.
4. A bunch of people already know English.