I take issue with the word "improve" there. Whilst I definitely agree that a common language is valuable in many ways, it would be preferable if a common language could be achieved without a loss of diversity (i.e. additional to, rather than replacing, the existing languages).
Different languages embody different cultures, and different ways of thinking. This diversity should be celebrated and embraced, not only as an aesthetic matter, but also because being able to communicate and think in different ways makes humans more capable.
Agreed - I have a few Shanghainese friends, and they tell me their parents discourage them from learning/speaking Shanghainese, since there is no "value" in doing so. They used to push them to learn English (but maybe that will change a little now). Perhaps they have a point, but when you're young and still good at learning language, you don't have to choose one or the other.
I have heard similar stories from Europeans coming from places with strong dialects / local languages, so it's not unique to China for sure.
Different languages embody different cultures, and different ways of thinking. This diversity should be celebrated and embraced, not only as an aesthetic matter, but also because being able to communicate and think in different ways makes humans more capable.