Here are some estimations based on different criteria:
* Native speakers: This is the most common definition, focusing on people who learned Mandarin as their first language. Estimates range from 936 million (according to Ethnologue) to over 1 billion (according to some Chinese government sources).
* L2 speakers: This includes people who learned Mandarin as a second language. Adding these speakers to the count significantly increases the total number, but estimations vary wildly.
* Total speakers: This includes both native and L2 speakers. There is no reliable estimate for this number, but it's likely in the billions.
It's important to note that:
* Regional variations: Mandarin, a member of the Sinitic languages, has many regional varieties, including Cantonese, Hakka, Min, and Wu.
* Mutual intelligibility: While these varieties are all considered Mandarin, they can be difficult for speakers of different varieties to understand.
* Dialect continuum: There is a gradual transition between the different varieties of Mandarin, making it difficult to draw clear boundaries.
Therefore, while we can estimate the number of native speakers, the total number of Mandarin speakers is much harder to pinpoint.