Isidore of Seville, Etymologies 9.1.4:
The Greek language however is considered the most renowned among the languages of the earth. For it is more sonorous than Latin and all other tongues, and it may properly be divided into five parts. The first is Koinu, that is mixed or common, which all people use. The second is Attic, that is the Athenian, which all of the authors of Greece used. Third is Doric, which the Egyptians and the Syrians have. The fourth is Ionic, and the fifth Aeolic, which they said people spoke in the Aeolic manner. There are certain distinctions in the respect of this type of Greek language, for thus is their speech divided.
Some say that there were four Latin languages, that is the Original, the Latin, the Roman, and the Mixed. The Original, which the most ancient people of Italy used under Ianus and Saturnus, is disordered as in the songs of the Salii. The Latin, which the Etruscans and everyone else in Latium used under Latinus and the kings is the language in which the Twelve Tables were written. The Roman began after the expulsion of the kings, from which Naevius, Plautus, Ennius, and Vergil, as well as the orators Gracchus, Cato, Cicero, and some others poured forth. The Mixed is what broke forth after the extension of the bounds of empire along with new customs and people into the Roman state, corrupting the integrity of the word through solecism and barbarism.
Graeca autem lingua inter ceteras gentium clarior habetur. Est enim et Latinis et omnibus linguis sonantior: cuius varietas in quinque partibus discernitur. Quarum prima dicitur KOINU, id est mixta, sive communis quam omnes utuntur. Secunda Attica, videlicet Atheniensis, qua usi sunt omnes Graeciae auctores. Tertia Dorica, quam habent Aegyptii et Syri. Quarta Ionica, quinta Aeolica, quas AIOLISTI locutos dixerunt. Et sunt in observatione Graecae linguae eiusmodi certa discrimina; sermo enim eorum ita est dispertitus.  Latinas autem linguas quattuor esse quidam dixerunt, id est Priscam, Latinam, Romanam, Mixtam. Prisca est, quam vetustissimi Italiae sub Iano et Saturno sunt usi, incondita, ut se habent carmina Saliorum. Latina, quam sub Latino et regibus Tusci et ceteri in Latio sunt locuti, ex qua fuerunt duodecim tabulae scriptae.  Romana, quae post reges exactos a populo Romano coepta est, qua Naevius, Plautus, Ennius, Vergilius poetae, et ex oratoribus Gracchus et Cato et Cicero vel ceteri effuderunt. Mixta, quae post imperium latius promotum simul cum moribus et hominibus in Romanam civitatem inrupit, integritatem verbi per soloecismos et barbarismos corrumpens.