* China is one country: It's not accurate to say there are multiple "countries" within China.
* Mandarin is the official language of China: This means it's the standard language used in government, education, and media.
* Many dialects exist: While Mandarin is the official language, China has many regional dialects, including Cantonese, Wu, Min, Hakka, and more.
To answer your question more directly:
* While Mandarin is the official language of China, not everyone speaks it as their native language.
* The vast majority of the Chinese population understands and can speak Mandarin to some degree.
* It's estimated that over 90% of the Chinese population can speak Mandarin.
So, while there's no official count of how many people speak Mandarin in China, it's safe to say that the majority of the population uses it in some capacity.