How should a non-native English presenter respond to a question they did not understand? I'm not an English native speaker, and my question is, probably, only relevant for non-native speakers.  

Sometimes, native speakers just don't care how easily the presenter can understand the question. Such a carelessness usually embarrasses the presenter enormously and makes him appear incompetent.  

What is the proper way to behave for the non-native speaking presenter? Is it OK to ask for a repetition?  

NOTE: I know, being a part of academic world requests some proper English knowledge. But you can hardly become as good as native speakers. And some native speakers have unusual dialects and use difficult expressions (sometimes, I bet, on purpose). I remember one speaker from Wales at a British conference. My God, that was Greek to me.
Yes, it is appropriate to ask the questioner to repeat the question, prefaced by:


  "I'm sorry but I didn't understand the question.  Can you repeat it or rephrase it?"


If you still don't understand it, you might ask someone else in the audience to restate it or rephrase it.



Some people at academic conferences are not good at asking clear, direct questions, even when they are native English speakers with normal dialect.  I have asked people to repeat or rephrase questions for this reason, and I am a native English speaker.