Google has released a new video aimed at helping webmasters make their sites available in more languages. The latest Webmaster Help video comes from Developer Programs Tech Lead Maile Ohye.
Specifically, the video discusses details about rel=”alternate” and its implementation on multilingual/multinational sites.
It's seventeen minutes long, so if you don't want to sit through the whole thing, there's a transcript on the video page that you can skim through.
Google provides a list of resources on the topic here.
If this is something that you're interested in, you may also want to check out this video from Matt Cutts from a couple years ago, when he discussed duplicate content and languages, and cautioned against using Google Translate to auto-translate your site.