There might be a language barrier; your English shows indications that it might not be your native language. Are there other languages you know better? Have you considered applying for categories there?
Not being a native speaker is not a bar to editing; you'll just have to be very very careful. Listen to the story-telling Bohemian (speil-czech), and so on.
If you're getting only a generic reply, then probably the answer to the "why was I rejected?" question is in the editors' guidelines (which you'll have to know anyway to edit, so go ahead and memorize them. Your application is the test.)