There is no such thing as "the Chinese language".
See also Chinese is hard, why learn it?
China is a big place with multiple ethnicities which have been forced to live under one dominant culture for a very long time. Even with that in mind, the distances between areas is so great that different areas developed their language differently from other areas. This means that people from different areas cannot understand one another at all.
"Learning Chinese" is about as meaningful as "learning European". There's no such thing.
In the west, there is an association between geography, language and culture which does not work very well for China. Since the Han Dynasty, China has developed a sort of consistency of culture and what the west would consider a common cultural myth. This is being continued and leveraged by the current administration, the Communist Party of China[doesn't exist], to maintain a coherent culture.
However, language is another problem entirely. Choosing any urban place, there tends to be two languages. One is a generally-intelligible regional language, and the other is a specific local language that diverges a bit. The local language can be considered a "dialect" of the larger regional language. Zooming out a little, regional languages share similarities when they are near one another, but local languages become increasingly different until locals from different places can't understand one another.
Government and merchants have needed a common language, which reinforces a lingua franca or common language. When the Han Dynasty took power, their preferred language was Mandarin Chinese which has stayed the dominant common language.
Writing in Chinese is very very old. So old that it was the language used by neighbouring cultures such as the Koreans and Japanese. Those cultures developed their own distinct written languages, and China's written language continued to evolve too. That ancient written lingua franca isn't in use anymore, but there is an old written form which is common throughout China using Traditional Chinese characters.
Even the Chinese think their written language is too difficult, and there have been several attempts to simplify the traditional forms. With the Communist Party's interest for literacy, there were strong efforts for simplification, resulting in the current Simplified Chinese characters.
The Communist Party has also made efforts to standardize spoken Chinese, recognizing the lingua franca nature of Mandarin Chinese, resulting in a revision of it called Standard Chinese. This is the language of government and business, and there is a Chinese proficiency test which the government uses.
So although there are many different languages, and "dialects", the fact that the major language has an offshoot that is officially recognized makes it hands-down the most important "Chinese" to learn.
So when referring to "Chinese", I mean this "Standard Chinese".
Learning it won't let you communicate in all places, unless those places have the common Mandarin Chinese in use, in which case it will be reasonably close. Literacy will be excellent, but only with Simplified Chinese and only occasional Traditional characters will be recognizable.
This is a reasonable first step in learning the language groups in China. The other steps would be to learn Mandarin Chinese itself, and to learn Cantonese, the by far distant second common language but the dominant one in Hong Kong and many distant Chinese communities since those people immigrated from primarily Cantonese-speaking communities. This isn't so important, as Hong Kong and everywhere else under the Chinese government's umbrella recognize Standard Chinese as an official language.
I'm also not interested enough to learn anything more than Standard Chinese and Simplified Chinese characters to pass a few of the proficiency tests. From there I'll be moving on to other languages, starting with Japanese.