Finch - Canonical URLs
This plugin is for multi-language sites where multi-language menus cause duplication of pages, resulting in duplicate content. It uses menu associations to resolve the canonical URL by adding a canonical link rel="canonical" to the page.
For example, if you had an site with English and Spanish and full menus for both, but your blog was only in English then you might end up with duplicate pages like this:
This plugin would add a canonical link to the Spanish page so that it wouldn't appear as duplicate content to search engines. You can set the canonical language, a canonical domain, and select which categories you want it to inspect. It adds a link to the category and articles in the category.