The problem is they need to learn a WHOLE new system of speaking. Don't spend too much time feeling sorry - concentrate on having the students speak HOWEVER THEY SOUND. The big question is can you and other accomplished speakers UNDERSTAND them. If you can then give them a big high five and move to the next lesson.
As a native speaker of English I hear lots of "bad" English but I can ofen figure out what the speaker wants to say. That is all that is required for communication.