This certainly isn’t my area of expertise, but I’ve been trying to figure out a way to integrate the Language Switcher plugin with a widget-enabled theme. As this hasn’t yet been implemented, I copied wrote the simplest of Widgets which will list the available languages on your blog in the sidebar.
There really isn’t anything special here, but for people even more hesitant with code than I am, pop this file into the wp-content/plugins/ folder of your WordPress installation, and then enable it via the Plugins admin page. You should then find the Widget available in the Presentation -> Sidebar Widgets admin page. At the moment, the Widget will display your available languages listed only by name. I’m still learning how to allow this to be changed from within the Sidebar Widgets page.
Click here to download Language Switcher Widget v1.0.