You can see it on redmine.org: If you use the search box you get lots of results but in all kind languages. As german native speaker it is not helpful to see results in russion or french (english is okay...). It should be possible to filter also for a certain language.

This is probably a bit more complex to realize. But I think it would be good to have wiki pages marked with a language somehow, so that they can be used as a filter when one search in the wiki.