Every person belongs to a speech community, a group of people who speak the same language. Estimates of the number of speech communities range from 3,000 to 7,000 or more, with the number of speakers of a given language ranging from many millions of speakers down to a few dozen or even fewer. The following list probably includes (in approximate descending order) all languages spoken natively by groups of more than 100 million people: North Chinese vernacular (Mandarin), English, Spanish, Arabic, Hindi or Urdu, Portuguese, Bengali or Bangla, Russian, French, Japanese, German, and Malay or Bahasa Indonesia. Roughly 120 languages have at least a million speakers, but some 60% of the world's languages have 10,000 or fewer speakers, and half of those have 1,000 or fewer speakers.
Many persons speak more than one language; English is the most common auxiliary language in the world. When people learn a second language very well, they are said to be bilingual. They may abandon their native language entirely, because they have moved from the place where it is spoken or because of politico-economic and cultural pressure (as among Native Americans and speakers of the Celtic languages in Europe). Such factors may lead to the disappearance of languages. In the last several centuries, many languages have become extinct, especially in the Americas; it is estimated that as many as half the world's remaining languages could become extinct by the end of the 21st cent.