10th millennium, or 10th century BC? Nobody has any clue what was going on in 10th millennium BC Greece. The very earliest languages we can posit are the pre-Indo-European substrates -- in Greece, these would be Eteocypriot, Eteocretan, maybe "Pelasgian," maybe "Lemnian," and, eventually, Minoan/Linear A. Everything we know about these substrates is from indirect evidence (for instance, place names in Greece that end in -unthos like the city Olynthos, destroyed by the Macedonians). None of these even come close to the 10th millennium BC, however. We have virtually no evidence of what was spoken in the Neolithic period, though Ringe has argued that there were most likely ultra-local "tribal" dialects or language branches with very little contact between them. Check here for a really fascinating "blog post" on the subject.