If only one language, such as English. You can communicate in this world than the people of billions of people. Where before it can communicate with other people, it must learn to understand first.
If you know only one language. For example: English You can communicate with people on Earth than a billion people. Prior to communicate with other people, you must learn to understand it.
If only one language, and language such as English. You can communicate people on earth has over a billion people. Which before they can communicate with others that need to study to understand it.