It's important to note that "most" can be defined in a couple of ways:
* Number of native speakers: Mandarin Chinese has the most native speakers, with over 1 billion people worldwide.
* Total number of speakers: However, if you include both native and non-native speakers, English has a larger number of speakers overall, due to its widespread use in international communication, business, and education.
So, depending on the definition of "most", the answer could be either Mandarin Chinese or English.