Wikinomics has a great post about the dominance of English on the Internet. The data and chart for the post come from the really useful www.internetworldstats.com, and in particular from its Languages reporting.
The chart above, and the stats on the website, show that 31% of Internet users by language are using English. Since 2000 the growth in the number of people using English has been 158%. However, the growth amongst many other language groups is greater. Chinese has grown by 470%, Portuguese by 525%, and Arabic by 940%.
Another way of looking at the stats is to compare how many people speak a language and how many of those are using the Internet. Amongst 129 million people estimated to speak Japanese, 67% are Internet users. Amongst other language groups the high scorers are: German (61%) and Italian (53%). Amongst the 2 billion English speakers only 18% use the Internet, and amongst the 1.35 billion Chinese speakers only 14% use the Internet.
I think we can take it for granted that this picture will evolve.