Well, using the u8 string prefix should work (at least with the source file in an encoding like UTF-16, on my machine) ...
char *Όνομα_μήνα(int μετρητής)
{
/*static */ const char *DATA[] =
{
u8"ΦΟΙΝΙΚΑΙΟΣ", u8"ΚΡΑΝΕΙΟΣ", u8"ΛΑΝΟΤΡΟΠΙΟΣ", u8"ΜΑΧΑΝΕΥΣ",
u8"ΔΩΔΕΚΑΤΕΥΣ", u8"ΕΥΚΛΕΙΟΣ", u8"ΑΡΤΕΜΙΣΙΟΣ", u8"ΨΥΔΡΕΥΣ",
u8"ΓΑΜΕΙΛΙΟΣ", u8"ΑΓΡΙΑΝΙΟΣ", u8"ΠΑΝΑΜΟΣ", u8"ΑΠΕΛΛΑΙΟΣ"
};
}
Otherwise I think there will be problems with Microsoft/Windows compatibility. I'm not sure it's 100%, but the current behavior seems to match MSVC.