I'm bored, so I'll bite. Yes, officially, Mandarin is the native language of the vast majority of China's 1.3 billion people. Unofficially, however, at most a large minority in China speak it natively. What is called a "dialect" in China often differs as much from standard Mandarin as, say, Romanian from Latin. Speakers of these dialects who live in large cities will often know enough standard Mandarin to get by, but usually only barely. Outside of mainland China and Taiwan the Chinese diaspora usually speaks either Cantonese or Fujianese languages like Hokkien. These languages are related to Mandarin, but certainly not mutually intelligible with it.
It's also a myth that the writing system is the same across Mandarin, Cantonese, Hokkien and all the other "dialects". While all "Chinese" languages use similar characters, written Chinese does not, in contrast to what is often thought, consist of pictographs. The written Chinese of a Cantonese speaker will therefore differ greatly from the written Chinese of a Mandarin speaker. Sometimes one version will merely seem "somewhat off" to a speaker of a different variety of Chinese, at other times it will make no sense at all.
With that in mind, the number of speakers of Mandarin has to be revised way, way down, to the point that it's no longer a serious contender for global language status. English is still supreme in that regard and will be for the foreseeable future, with Spanish coming in second.
There is a non-zero chance of China becoming a larger economic player. Also, China exports a lot of immigrants to other countries. I don't have any data to back this up, but it does not seem like an totally 'out there' idea.
