[originaltext] The number of speakers of English in Shakespeare’s time is es

The number of speakers of English in Shakespeare’s time is estimated to have been about five million. Today it is estimated that some 300 million people speak it as a native language, mainly in the United States, Canada, Great Britain, Ireland, South Africa, Australia and New Zealand. In addition to the standard varieties of English found in these areas, there are a great many regional and social varieties of the language as well as various levels of usage that are employed both in its spoken and written forms. In fact, it is impossible to estimate the number of people in the world who have acquired an adequate working knowledge of English in addition to their own language. The purpose for English learning and the situations in which such learning takes place are so varied that it is difficult to explain and still more difficult to judge what forms an adequate working knowledge for each situation.
    The main reason for the widespread demand for English is its present importance as a world language. Besides serving the indefinite needs of its native speakers, English is a language in which some of important works in science, technology and other fields are being produced, and not always by native speakers. It is widely used for such purposes as airport communications, international conferences, and the spread of information over the radio and television networks of many nations. It is a language of wider communication for a number of developing countries, especially former British colonies. Many of these countries have multilingual populations and need a language for internal communication in such matters as government, commerce, industry, law and education as well as for international communication and for entrance to the scientific and technological developments in the West.
19. What is the speaker mainly talking about?
20. According to the passage, what is hard to estimate about English?
21. Why do some former British colonies widely use English?