hanasemasen = can't speak
hanashimasen = don't speak
It's arguably more proper to say "nihongo ga hanasemasen" (I can't speak Japanese) than "nihongo wo hanashimasen" (I don't speak Japanese). The first is a statement of my personal abilities. The second could easily be a statement of my attitude. "nihongo ga hanasemasu kedo nihongo o hanshimasen" (I can speak Japanese but I don't speak Japanese)
For whatever reason I've never heard wakaremasen (can't understand) but only don't understand (wakarimasen).