Maybe not a single common language, but there needs to be a limited set at least. People have to be able to have person-to-person conversations. Maybe that takes the form of a few languages where people are fluent in enough languages that they can speak at least one of the same languages as another person they meet. Or a perhaps there are local languages, with a single lingua franca. Then there’s the easiest, where there is one dominant language that is spoken by nearly everyone, at least to some extent. Personally I kind of prefer the lingua franca approach, but I wish a constructed language would finally gain wider popularity. Could be Esperanto, could be something that took some lessons from the imperfections in Esperanto.
Or, if you count the speakers worldwide, Chinese would be the choice … :D
No, English has far more speakers than Chinese. They’re just mostly L2 speakers, with Chinese speakers intensely concentrated inside China. Chinese and English are basically mirror images of each other. Almost all Chinese speakers are L1 inside China, whereas English has over a billion L2 speakers. Meanwhile Chinese has under 200 million L2 speakers and English has a little over 300 million L1 speakers.
There is no “Chinese“. Mostly a “Chinese” means mandarin, which is spoken in and around Beyjing, when I remember it correctly. The next “Chinese” would be cantonese, which is as far away from mandarin as english to russian.