How should a non-native English presenter respond to a question they did not understand?
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.