“Have a nice day”—this is how Iranian President Hassan Rohani concluded his phone conversation with US President Barack Obama, the first direct contact between leaders of the two nations in over three decades. A message on Rohani’s Twitter page, which has since been deleted, stated that Obama answered in Farsi by saying “khodahafez” to indicate goodbye, whose literal meaning is “may God be with you.” The tweet was one of several Rohani posted after the historic phone conversation. He noted that Obama had phoned him and told him he was positive that relations between Iran and the US would have...