The controversial issue, whether Epirotan Ethnes spoke greek has already mentioned previously inside this book. Its obvious that the Greek language was spoken during all Dark age in Dodona and in Nekromanteion. The latter was considred always as one of the Greek manteia (Herod. 1.46.3 where he talks about the “greek manteia” and the meeting of Herod. with the delegates of Periander is described as a normal action (Herod. 5.92)
The Cassiopeians likely spoke greek in that era, because the daughters of Aenieans went to offer worship among them and Molossians, who took part on Ionian immigration were obviously greek speaking, according to Herodotus.
The royal family of Molossis, mainly spoke greek and its members were considered Greeks from Pindarus, Herodotus and Thucydides, but they were not pure. These one way or another are just straws in the wind. The real evidence has came only with the recent discovery of the inscriptions of 370/368 BCE. They are completely in Greek, the names are Greek and the ethnes which are represented to these inscriptions are Molossian and Thesprotian. Greek language and greek names werent adopted suddenly before Peloponessean war. These ethnes were speaking Greek even before the time of Thucydides. We can conclude confidentially that Thucydides put the label “barbarians” onto the ethnes of S. Epirus, without any secondary meaning of non-Greek speakers anyway. They could spoke a more ancient form of Greek language – like the “other Amphilochians” who are too difficult to exist as a carrier of non-greek ethnes between the Greek speaking ethnes of S. Epirus, North Aetolia and Akarnania.