Quote Originally Posted by Hanna View Post
I understand Russian a lot better than I can speak it.
I think this goes for any language
I know a guy who writes in English the way that native speakers couldn't tell him apart but sometimes he can't answer simple question

From my personal experience (and from what I heard from other people) it is one of the stages of learning foreign language by adult. You learn to the point you can understand but can't talk and then you keep on this plateau and then you need a little push and you start talking.
Some people can't start talking for years because they need harder push (change of the environment)