Francesco Filelfo, Letter to Lorenzo Medici (Part 19)
“One who wishes to seem and to be an eloquent man whether among the Greeks or the Romans should study with all his care that he hold onto the language that is most elegant in either tongue.
In this matter, I may toot my own horn, because I employed the assistance of no Latin person, but learned by my own industry and diligence both Greek and Latin (first the simple language and then the language of literature), so that I see that I pursued a thing which happened to no one else from all of human memory up to this time, namely, that no less in verse than in prose, in both Greek and in Latin, in common and in literary speech (as they call it now), I labored over and published so many volumes that now it is easier in some way to write in Greek than in Latin or Italian.”

Qui virum se eloquentem et haberi et esse voluerit, sive apud Graecos, sive apud Latinos, huic omni cura studendum est, ut in utrisque eam teneat linguam, quae sit elegantissima.
Quibus in rebus illud mihi gloriari licet, quod nullius latini hominis usus adminiculis, sed industria solum diligentiaque mea, ita et graecam et latinam tum linguam tum litteraturam didicerim, ut me videam consecutum quod nemini unquam ex omni hominum memoria in haec tempora contigerit, ut non minus versu quam soluta oratione, et graece et latine, tam vulgari quam litterali eloquio, quod hoc tempore appellant, quam plurima volumina elucubrarim atque aediderim, ut iam mihi facilius sit quodammodo graeco sermone scribere quam latino ac nostro.