In China, Mandarin is China's mother tongue. In Britain, what is the mother tongue of Britain? someone says that

In China, Chinese is the mother tongue of China people. In Britain, English is the native language of British people. English is the most widely used way of communication in the world. For environmental reasons, the easiest language to learn is one's own mother tongue. As far as foreign languages are concerned, English is widely used for historical and political reasons, not because it is the easiest to learn. Chinese is one of the most difficult languages to learn, but it is used by the most people.