Let me point out the obvious; that is, the title of this submission is slightly misleading as this is not a chart of the number of internet users by language, it's a chart of the number of internet users by country of residence. There's no such language such as "US" or "UK", and while there are many notable differences, I wouldn't consider UK English and US English different languages. Obviously, there's also no "Indian" or "Chinese" language.
Misleading. Having lived in China I can tell you that an Internet user there is nowhere near equivalent to an Internet user in the US in terms of how often and to what extent they use the Internet.
Very nice. But how come Brazil has more internet users than Germany and India but it shows as having a smaller percentage of the world's internet users?
If we're counting this by language, we should figure out how much Ukrainians (or Belorusians) use internet in russian language, primary, and how much don't; and then we should sum up those numbers.
Everything else would be a speculation.
I guess this is a somewhat interesting chart, but it's got nothing to do with language except one unqualified prediction about what languages will dominate a future Internet.
Please title your post more appropriately.
Now, about the chart itself...
How did the authors fail to sample Russia - the most demographically significant userbase between N.A/Europe and China/India?