What language would the Persian and Greek diplomats have used to communicate?
Well, persians conquered the Ionian city states from Turkey, so I'm sure many people knew greek at the time. There's an article which says how the first contact between greek and persians went. You really can't find a persian source on how they viewed greeks after the Greco-persian wars, but Persia did supported division at the region, even Sparta was allied during a time with Darius II http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0009%3Achapter%3D8%3Asection%3D1