It is highly unlikely Chinese will displace English as a lingua franca, in the near future. There will be more Chinese pages or more Chinese internet users, perhaps, but that will not make the dominant language of the "internet" Chinese. For the rest of the world, English will remain the dominant language. Chinese users wanting to speak to most non-Chinese will need to resort to English or another third language.
As for "preserving the purity" of the language, that's just bullshit. TV shows and such are subtitled in Chinese for two very simple reasons: first, many Chinese
don't speak Mandarin Chinese, the official language! Most Chinese dialects are mutually unintelligible. Only the written language is common to the whole of China, and allows communication between users/people who don't speak the same (oral) language.
Second, it also promotes integration into mainstream society by ethnic minorities. Some call it cultural genocide, but in America we (the American government) promote ESL and only offer most classes in English, just as Germany promotes German language education. Hardly preserving the purity of the language; it is more directed and cultivating a sense of national character, by everyone having a common language, and also making sure everyone can understand what's being said. Dialects (and people who can't understand English) are far too common not to demand translations and subtitles.
So what is the author saying? Inferring that whichever language group has the most users, dominates the internet? I'm sorry, but Chinese users aren't anywhere near a 50% majority, much less any sort of "overwhelming" majority. English has a huge number of users; many of the users who speak Spanish, German, Japanese, Russian, and even Chinese are also part of the English hegemony. And the participation of these groups in the English internet is what makes it dominant, not its number of users.