How should I respond to the errors of my English learners in English or the native language for them to understand more?

If their answer is close to the right one, tell them so.

If it is completely wrong, tell them the right answer and why.

I do agree with what has been mentioned above by Zuleigha Abderoef . Beside, as English teachers we should ignore students' errors in order not to frustrate students by focusing on errors and rather help them trespass such errors by involving all possible audio-visual aids.  

If it is a matter of listening and speaking,here the role is yours you just need to read words correctly to your students and explain new ones to them using your board . But considering grammar ,your role is explaining rules in the most easiest way using your easy english if they are foreign students.

You should try to stick to English. There must be a simpler paraphrasing or at most difficult situation a drawing would help not only to explain but also to keep the meaning in English in the student's mind.

It depends on the situation. If its a reading lesson and the student pronounces incorrectly or struggles - you can help him or her along. New words in the text can be explained using whiteboard and real life incidents. In my personal experience I find that teaching for example complex grammar rules (as well as regular everyday grammar) are much easier understood by student body if supported with their native language. But dont get into the habit of explaining in their native language because they quickly get used to this method and then start to depend upon it. Keep everything pristine and English until you sense a certain 'block' from students. This is usually manifested by blank stares and from more active students a definite verbal indication 

Paraphrasing the error or explaining it in a more simple language.