Wiktionary
n. (context literature English) A language spoken and written in formal speeches, literature, the arts, etc.
Wikipedia
A classical language is a language with a literature that is classical. According to UC Berkeley linguist George L. Hart, "it should be ancient, it should be an independent tradition that arose mostly on its own, not as an offshoot of another tradition, and it must have a large and extremely rich body of ancient literature."
Classical languages are typically dead languages, or show a high degree of diglossia, as the spoken varieties of the language diverge further away from the classical written language over time.
Usage examples of "classical language".
In devising theories, physicists often start by working in a purely classical language that ignores quantum probabilities, wave functions, and so forth—.
The great body of Buddhist literature in the Indian classical language, Sanskrit, which has no affinity with Tibetan, was translated into Tibetan so that by the end of the thirteenth century Tibetan Buddhists had ceased to be directly dependent on Indian religious authority.
There was never time, the way things went for me, to learn a classical language.
Sandbag promptly astonished his companions with a flashback to his compulsory classical language courses, which neither Jack nor Dr Langer would have dreamed he had retained, even in this age of intensive secondary education.