The people in the old movie pronounced Harkonnen the obvious way from the spelling, /har-KOH-nen/, so I was confused when the people in the new movie said it differently. The trailer slightly annoyed me, to be honest.
But then I heard an interview with Frank Herbert, and he pronounced it like HΓ€rkΓΆnen with an American accent, /HAR-konen/, so that's it, voice of God.