While Mandarin is spoken by the most people as a native language, English is most widely used worldwide. Mandarin is relatively concentrated, primarily spoken natively in East Asia. English on the otherhand, is spread out, primarily from the British empire's colonization. Even in places where the British didn't colonize, the rise of the Internet and the US has made English a prized second language. People in China are taught English as a second language while they are young. Go anywhere in the world and you will find almost everywhere people that have basic knowledge of English. While it is not the language with the most native speakers, English is very widespread. It is considered a Lingua Franca, a language used to make communication between persons not sharing a native language or dialect.[1] The word itself is based on French when French was used as a common language. English is typically used around the world between people as a go-to when they don't speak the same language. It is the primary language used internationally for business, politics, etc. Thus, it has in fact beat Mandarin in worldwide use, used as a second language for communication worldwide.

[1] https://en.wikipedia.org/wiki/Lingua_franca