China is the most populous country on the planet with some 1,4 billion inhabitants. We all know that the Chinese speak Chinese. In reality, however, there are several (probably hundreds) forms of Chinese, Wu, Yue (Cantonese), and Mandarin being some of the big ones. In addition to that, a lot of other languages are spoken in China.
In China, around 70% of the population speaks some form of Mandarin, but the different dialects of Mandarin aren't always mutually intelligible. Among the older demographic, minorities, and in rural areas, Mandarin isn't as common and other languages are spoken, but within the next few decades, the proportion of Mandarin speakers might grow.
The fact of the matter is, though, that different Chinese languages are (mostly) unintelligible between each other. Someone who speaks Mandarin won't necessarily understand a Cantonese speaker, for example.
In fact, even Mandarin specifically has numerous different dialects that aren't all mutually intelligible! Mandarin speakers in Taiwan (in the South) and Beijing (in the North) or other dialects further from the North are very different and not at all mutually intelligible.
So the question becomes difficult to answer. Yes, most Chinese (70%) do understand a form of Mandarin (even though they might speak a regional language as their first language) - but which variant of Mandarin do they speak?
What Other Languages Are Spoken In China?
China covers a vast territory and is the home of 1.4 billion people. It should come as no surprise that the Chinese people speak a wide range of different languages.
More than 11 different language families and branches are represented in China. The bigger ones are obviously the Sino-Tibetan language family, which includes Mandarin, Cantonese, and many others.
But hundreds of other languages of many other groups are present in the country, some are even spoken by several million.
To name a few of the language families spoken in China and some of the languages within those groups, there are:
Sino-Tibetan languages such as Mandarin, Cantonese, Wu, Hakka, but also more remote languages such as Tibetan or Burmese. (And many others).
Kra-Dai languages which include such languages as Dong, Gelao, Li, but also a wide range of "Tai" languages, of which Thai, the language of Thailand is a part. Thai, itself, isn't commonly spoken in China, however.
Turkic languages such as Uyghur, Uzbek, Kazakh, Tartar, and many others. (Did you know that the early, ancestral language of modern-day Turks was actually influenced by Chinese at some point?
Mongolic languages like Mongolian, Oirat, and Buryat
Tungusic languages such as Manchu, Xibe, and Evenki.
Korean - A Koreanic language - spoken by mostly Korean immigrants and their children in China. A surprisingly high number of Korean speakers actually live in China. (2.3 million).
Hmong–Mien like Hmong and Mien (obviously) but also languages such as Miao, Mien, and She.
Austroasiatic languages like Palung De'ang, Wa, but also Vietnamese which is spoken in China by a smaller Vietnamese community, just like Mandarin is spoken in Vietnam by some.
Austronesian languages like Tsat and the Formosan languages that are spoken in Taiwan.
Indo-European languages like Russian (in Northern China), Portuguese in Macau, and English in Hong Kong.
And these just represent a small selection!
Conclusion: Do All Chinese Speak Mandarin?
So the answer is definitely no. Not everyone in China speaks Mandarin. Only about 70% of them do. The rest speak either other local languages, immigration languages or languages that have come to the region in the time of colonization.
Despite this, Mandarin is the most widely spoken primary language on the planet. Besides China, Mandarin is spoken in several Asian countries, and there are sizeable communities of Mandarin speakers all over the world.