Back in April 2005, Technorati started automatically tracking the primary language of each blog that we tracked. We did this so that we could easily allow people to filter out posts in languages other than their native language. This is available in a pull-down menu on every search results page. We also wanted to get some idea of where the worldwide growth of blogging was taking place, and what trends we could glean from the data.
He includes a bunch of caveats in his report, but he also includes a bunch of awesome charts.