Cretes and Arabians. These two groups “seem to have been added to the list as an afterthought” (Knowling). Crete is an island to itself and Arabia was separate also though near Judea and full of Jews. The point is not that each one of these groups of Jews spoke a different language, but that wherever there was a local tongue they heard men speaking in it.
We do hear them speaking (akouomen lalountōn autōn). Genitive case autōn with akouō the participle lalountōn agreeing with autōn, a sort of participial idiom of indirect discourse (Robertson, Grammar, pp. 1040ff.).
The mighty works (ta megaleia). Old adjective for magnificent. In lxx, but only here (not genuine in Luk 1:49) in the N.T. Cf. 2Pe 1:16 for megaleiotēs (majesty).