It was a claim like this that motivated me to begin studying Chinese back in the 1970s. But if we are talking about one language community, all of whose members can genuinely converse with one another, today English just might have more speakers than (standard) Chinese has. Social science surveys by the Chinese government suggest that only just more than half of China's population is conversant in standard Chinese,

http://news.xinhuanet.com/english/2007-03/07/content_5812838...

and that squares with the experience of most travelers in China, and most Chinese-speaking people who know a lot of Chinese people outside of China, that there are still quite a few nationals of China who are not readily understood when they attempt to converse with other nationals of China.

Influence of a language depends on a lot more than just raw number of speakers. Sometime way back in the early 1980s, the Xerox company did an estimate of language influence weighted by the per-capita domestic product of persons speaking various languages, which of course boosts the ranking of English (and also of Japanese, at that time) as compared to Chinese.

Looking at what happened to Russian (my apologies to the authors of the first couple comments posted here), I would actually expect the influence of Chinese to decline by 2050, while the influence of English, both from the core strengths of the "inner circle" English-speaking countries (Britain, the United States, Canada, Australia, Ireland, and New Zealand) and the outer circle of countries where English is co-official, and from the unparalleled use of English as a worldwide interlanguage. When someone from Korea meets someone from Japan while both are in Taiwan, either might speak the language of the other, and I have seen that done both ways, but when they want to include a local person in the conversation, unless they really are in Taiwan as students of Chinese, they will likely resort to English to speak to one another. And so it goes with all kinds of unlikely combinations of ethnic groups in all kinds of places all over the world.

I am not at all ethnocentric about my sole native language, General American English, and I am second to none in urging Americans to acquire other languages for additional international understanding, but every mash-up of language groups that happens day by day in today's world is likely to accelerate the spread of English and to increase its influence.