Mandarin

• China is becoming the second largest economy in the world, based on purchasing power. And there are 880 million speakers of Mandarin, or 20 percent of the world's population. As more countries do business with China, and more people travel to China, Mandarin is becoming a useful language to learn.
  
  

English

• English is the most widely used language of business, commerce and the Internet. And is the primary secondary language learned in most countries. English is still the most useful language to learn.
  
  

Spanish

• There are approximately 350 million natural speakers of Spanish in the world. And it's becoming the secondary language spoken in the United States. It is also the language of trade and commerce in 20 countries. It is a useful language to learn, especially in the United States.
  
  

French

• French is the working language of the United Nations and is a secondary language in Europe and North Africa. It is therefore a useful language to learn.