For instance one of the problems I encounter is the following: If a faq has questions in both english and french, when a german user comes in, he sees an empty faq...
Maybe there should be a better visibility of existing questions in the faq.
For instance on the main page, if there is no category in the language, add links to "english categories" and "french categories" (for all languages where there are categories).
And the same with questions... add links to questions of foreign languages on the main page.
For the sitemap too, there could me a message "here you can browse through the current_language questions" and maybe add "see below for other languages" and put at the bottom a link to the foreign non-empty sitemaps?