Thanks to Dennis Baron's post to ads-l yesterday (which you can also read here), many of us have been reminded that it's "International Mother Language Day", so designated by UNESCO. The folks at UNESCO have done a pretty massive Atlas of the World's Languages in Danger, with nice interactive mapping, pretty extensively updated and developed since the earlier versions, if memory serves. These maps are always fraught with problems, even when they're done by really good specialists, and it would be easy to nitpick about how 'unsafe' the status of Welsh is or whether Hawaiian is best counted as 'critically endangered' or not. Personally, I'm not always comfortable with what counts as a language in various cases.
But this isn't a place for a lot of griping: it's a very nice and powerful tool. You can zoom in to places, as you see below for Belgium and surrounding areas (showing the rollover on Walloon here), display languages by estimated numbers of speakers, etc.
So, happy International Mother Tongue Day. I'll be speaking mine some today, if the phone lines to the home country are working.