It's a shame that people think that having a common national language has to come at the expense of local languages/dialects.
Compare the language policy of China with that of India, where even though Hindi and English are nominally the languages on a national level and all students are in theory taught at least one of them, the government doesn't try to actively suppress other local languages in schools or media.
As a result, an educated Indian is often trilingual in English, Hindi, and their local language, whereas in mainland China, knowledge of non-Mandarin dialects is decreasing in the younger generations.
Compare the language policy of China with that of India, where even though Hindi and English are nominally the languages on a national level and all students are in theory taught at least one of them, the government doesn't try to actively suppress other local languages in schools or media.
As a result, an educated Indian is often trilingual in English, Hindi, and their local language, whereas in mainland China, knowledge of non-Mandarin dialects is decreasing in the younger generations.