NOT A TEACHER
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Hello, GoodTaste!
It all depends on what you want to communicate. There are a few options I can think of:
A) The global population of speakers.
B) The population of people who speak English as a second language.
C) The number of countries in which English is spoken as either the first or the second language by more than an arbitrary percentage of the population.
D) How often conversations between people from different countries are in English.
E) How many words spoken by every person in the world per hour are in English compared to other languages.
Mandarin has a huge population of native speakers, but English has a ginormous population of foreigners who can speak it as a second language.
Is "English is the most widely spoken language in the world" correct if I mean C, D?