New Patch: WordPress 2.7 for Language Switcher
In order to use the Language Switcher plugin to create a multilingual site in some versions of WordPress, you need to "patch" the core files of WordPress (i.e. modify them with some updates that haven't yet gotten into that version of WordPress).
I've released a patch file for WordPress 2.7, which fixes some issues in feed URLs. You can download it on the Language Switcher plugin page.