The standard Chinese dialects (or languages) spoken in Mainland China and Taiwan are Mandarin, Wu, Yue, Minnan, and Xiang. Of these six languages, Mandarin is spoken by more than 70% of mainland Chinese and is taught as a second common language to speakers of other Chinese varieties.
So when we talk about Chinese, it is usually taken to mean Mandarin unless otherwise specified. The different 5 Chinese types combined account for only around 30% of speakers in China, while they are also official languages in their respective regions as well. They are therefore called minority languages or regional languages. Each region has its language variation, with some differences being so significant that people from the different areas cannot understand each other even if they speak the same variety of Mandarin.
Despite all these differences, Mandarin has still considered one language due to mutual intelligibility between its variations, which means that if you can speak one take, you can easily understand another variation even though it may sound slightly different from what you’re used to hearing. This characteristic makes Chinese unique among significant world languages where many varieties have become separate languages over time because people could no longer understand each other after migration or colonization.
In contrast, all these different Chinese varieties can be traced back to Old Chinese, which was spoken at least 2,000 years ago. Therefore speaking Mandarin does not take precedence over any other form of Chinese but instead refers to a single branch within an already existing family tree of closely related languages.
Some argue that since there are several billion Cantonese speakers in the world and there are only 1 billion Mandarin speakers, then Cantonese should be considered as a language instead of just being part of Chinese which is viewed as synonymous with Mandarin by most non-Chinese people.