Over on WSJ.com there is an interesting essay on what the author, a linguist named John McWhorter, thinks will happen with the world's languages in the future. His main argument is that there will be fewer languages but the remaining ones will be simplified from their current versions.
As he points out:
Science fiction often presents us with whole planets that speak a single language, but that fantasy seems more menacing here in real life on this planet we call home—that is, in a world where some worry that English might eradicate every other language.
McWhorter speculates that there may be as few as 600 distinct languages in 2115 with English being the dominant one while explaining why it won't be Mandarin Chinese. While he is not pleased with the idea of losing so many languages McWhorter also points out an up side as well.
A future dominated by English won't be a linguistic paradise, in short, but it won't be a linguistic Armageddon either.
The whole thing is worth a read.
Top image of Tower of Babel from Wikipedia