Thanks, Contribute/fi works now. The other thing was "Category:Translator Help" page where should have been "Contribute" and "Contribute/fi" links, too.
That page is dynamically created, taking links from the pages themselves. Please do not use Contribute/fi as the category, but Osallistuminen/fi - which is the translation used on UserBase. You can see the agreed category translations on http://userbase.kde.org/Category_Translation,_Esperanto_to_Suomi(fi) - if you think we should copy these pages to TechBase I'm happy with that suggestion. The advantage of doing it this way is that if someone hits the category link at the bottom they will see pages in the required language, not Contribute, for instance, in 30 different languages.