Isidore of Seville, Etymologies 9.1:
The diversity of languages arose in the construction of the tower after the flood. Before the arrogance of that tower divided human society into diverse sounds and significations, there was one language of all peoples, which was called Hebrew. The Patriarchs and the Prophets used it not only in their sermons, but also in their sacred letters. But at the beginning, there were as many languages as there were peoples, and then more peoples than there were languages, because many different groups of people arose from one language.
Languages are so called in this place from the words which are made by the tongue (per linguam), by that sort of locution in which that which makes something is named by the thing which is made; thus ‘mouth’ is often used for words, just as ‘hands’ for letters.
There are three sacred languages: Hebrew, Greek, and Latin, which are the most outstanding in the entire world. For in these three languages, the case of the Lord was written upon the cross by Pontius Pilate. For this reason, and on account of the obscurity of Sacred Scriptures, the understanding of these three languages is necessary so that you may reference one of the others if an expression in one of the languages presents some doubt to your mind about the meaning of a word or its interpretation.
Linguarum diversitas exorta est in aedificatione turris post diluvium. Nam priusquam superbia turris illius in diversos signorum sonos humanam divideret societatem, una omnium nationum lingua fuit, quae Hebrae vocatur; quam Patriarchae et Prophetae usi sunt non solum in sermonibus suis, verum etiam in litteris sacris. Initio autem quot gentes, tot linguae fuerunt, deinde plures gentes quam linguae; quia ex una lingua multae sunt gentes exortae.
Linguae autem dictae in hoc loco pro verbis quae per linguam fiunt, genere locutionis illo quo is qui efficit per id quod efficitur nominatur; sicut os dici solet pro verbis, sicut manus pro litteris.
Tres sunt autem linguae sacrae: Hebraea, Graeca, Latina, quae toto orbe maxime excellunt. His enim tribus linguis super crucem Domini a Pilato fuit causa eius scripta. Vnde et propter obscuritatem sanctarum Scripturarum harum trium linguarum cognitio necessaria est, ut ad alteram recurratur dum siquam dubitationem nominis vel interpretationis sermo unius linguae adtulerit.