Yahoo wants to make every language feel like English. Enter your query in your language and the search results will include not just the web pages written in your language, but also web pages written in other languages. For example, you'll be able to find this blog post if you search for [Recherche multilingue Yahoo], even if I didn't include these French words. And when you click on the results, you'll see this blog post translated in French.
The multilingual search is available at Yahoo! France and Yahoo! Germany. You just have to activate "Recherche multilingue" or "Suche Translator" option. The search results will include pages written in French, English, German, Spanish and Italian.