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.
In the context of traditional European classical studies, the "classical languages" refer to Greek and Latin, which were the literary languages of the Mediterranean world in classical antiquity.
In terms of worldwide cultural importance, Edward Sapir in his book Language, would extend the list to include Chinese, Arabic, and Sanskrit:
When we realize that an educated Japanese can hardly frame a single literary sentence without the use of Chinese resources, that to this day Siamese and Burmese and Cambodgian bear the unmistakable imprint of the Sanskrit and Pali that came in with Hindu Buddhism centuries ago, or that whether we argue for or against the teaching of Latin and Greek [in schools,] our argument is sure to be studded with words that have come to us from Rome and Athens, we get some indication of what early Chinese culture, Buddhism, and classical Mediterranean civilization have meant in the world's history. There are just five languages that have had an overwhelming significance as carriers of culture. They are classical Chinese, Sanskrit, Arabic, Greek, and Latin. In comparison with these, even such culturally important languages as Hebrew and French sink into a secondary position.
In this sense, a classical language is a language that has a broad influence over an extended period of time, even after it is no longer a colloquial mother tongue in its original form. If one language uses roots from another language to coin words (in the way that many European languages use Greek and Latin roots to devise new words such as "telephone", etc.), this is an indication that the second language is a classical language.
In comparison, living languages with a large sphere of influence are known as world languages.
The following languages are generally taken to have a "classical" stage. Such a stage is limited in time and is considered "classical" if it comes to be regarded as a literary "golden age" retrospectively. Thus, Classical Greek is the language of 5th to 4th century BC Athens and, as such, only a small subset of the varieties of the Greek language as a whole. A "classical" period usually corresponds to a flowering of literature following an "archaic" period, such as Classical Latin succeeding Old Latin, Classical Sumerian succeeding Archaic Sumerian, Classical Sanskrit succeeding Vedic Sanskrit, Classical Persian succeeding Old Persian. This is partly a matter of terminology, and for example Old Chinese is taken to include rather than precede Classical Chinese. In some cases, such as those of Arabic and Tamil, the "classical" stage corresponds to the earliest attested literary variant.
Antiquity
Classical Sumerian (literary language of Sumer, c. 26th to 23rd centuries BC)
Middle Egyptian (literary language of Ancient Egypt from c. the 20th century BC to the 4th century AD)
Old Babylonian (The Akkadian language from c. 20th to 16th centuries BC, the imitated standard for later literary works)
Middle Assyrian (The Akkadian language from c. 16th to 13th centuries BC)
Classical Hebrew (the language of the Tanakh, in particular of the prophetic books of c. the 7th and 6th centuries BC)
Classical Aramaic (the administrative language of the Achaemenid Empire, 6th to 4th centuries BC)
Classical Chinese (based on the literary language of the Zhou Dynasty from c. the 5th century BC)
Classical Greek (Attic dialect of the 5th century BC)
Classical Sanskrit (described by Pāṇini's grammar, but used since c. 4th century BC)
Classical Tamil (Sangam literature c. 2nd century BC to 2nd century AD, defined by Tolkāppiyam)
Classical Pali (Buddhist Canon used this language from 2nd centuries BC)
Classical Latin (literary language of the 1st century BC)
Classical Mandaic (literary Aramaic of Mandaeism, 1st century AD)
Classical Syriac (literary Aramaic of the Syriac church, 3rd to 5th centuries)
Middle Persian (court language of the Sassanid Empire, 3rd to 7th centuries)
Classical Coptic (language of Egypt and the Coptic Orthodox Church of Alexandria, 3rd to 13th centuries, liturgical language to the present day)
Middle Ages
Ge'ez (language of the Ethiopian Orthodox Tewahedo Church, the Garima Gospels are dated from the 5th century to the 10th century by various scholars)
Classical Armenian (oldest attested form of Armenian from the 5th century and literary language until the 18th century)
Classical Arabic (based on the language of the Qur'an, 7th century to present)
Classical Kannada (court language of Rashtrakuta empire, earliest available literary work is the Kavirājamārga of 850 AD)
Old Saxon (language of Saxon Christian literature, 9th to 12th centuries)
Old Javanese, (from the 9th century to 15th century)
Old English (language of Beowulf and the Anglo-Saxon Chronicle with many divergent written dialects, but partially standardized in West Saxon form)
Classical Georgian (language of the Georgian Golden Age, 9th to 12th centuries)
Old East Slavic (language of the Kievan Rus', 9th to 13th centuries)
Angkorian Old Khmer (language of the Khmer Empire, 9th to 14th centuries)
New Persian (language of classical Persian literature, 9th to present)
Old Nubian (language of Nubia, 9th or 10th to 15th centuries)
Old Bulgarian (language of the First Bulgarian Empire during its Golden Age, 10th century, earliest manuscript is Freising manuscripts)
Classical Tibetan (religious and literary language of Tibet, 10th century to present)
Classical Japanese (language of Heian period literature, 10th to 12th centuries)
Classical Occitan (language of the troubadours, 11th to 14th centuries)
Classical Tagalog (Language of the Mai State, Kingdom of Tondo, central and entire Southern Luzon during the Classical Period-c 900 AD-14th century)
Middle High German (language of Medieval German literature, 11th to 14th centuries)
Old Serbian (language of Serbia before its conquest by the Ottoman Empire, 11th to 14th centuries)
Classical Telugu (The earliest available literary work is the Telugu Mahabharata, 1067 AD)
Malayalam language (The earliest extant prose work is the Ramacharitam, 12th century)
Old Norse (language of the Viking Age, from the 12th century)
Middle Bulgarian (language of the Second Bulgarian Empire, 12th to 15th centuries)
Middle Low German (language of the Hanseatic League, 12th to 17th centuries)
Classical Icelandic (the language of the Icelandic sagas, 13th century)
Classical Catalan (language of literature in Aragon, 13th to 14th centuries)
Classical Manding (language of the Mali Empire, 13th to 16th centuries)
Old Ruthenian (one language of the Grand Duchy of Lithuania, 13th to 16th centuries)
Old Anatolian Turkish (11th to 15th centuries)
Classical Ge'ez (language of Golden Age of Ge'ez literature, 13th to 16th centuries)
Classical Irish or Classical Gaelic (language of the 13th to 18th centuries Scottish and Irish Gaelic literature)
Classical Wolof (language of the Wolof Empire, 13th to 19th centuries)
Middle English (language of The Canterbury Tales, 14th to 15th centuries, with many divergent written dialects, but partially standardized based on London speech)
Classical Hungarian (language of Hungarian literature, 14th to 15th centuries)
Classical Songhai (lingua franca of the Songhai Empire, 14th to 16th centuries)
Early New High German (language of the Holy Roman Empire, the German Renaissance, and the Protestant Reformation, 14th to 17th centuries)
Classical Malay (language of Maritime Southeast Asia, 14th to 18th centuries)
Middle Oriya (language of Odia literature, 14th to 19th centuries)
Chagatai (classical Turkic language of Central Asia and the Volga, 14th to early 20th centuries)
Pre-Colonial Americas
Classical Maya (the language of the mature Maya civilization, 3rd to 9th centuries)
Classical Quechua (lingua franca of the 16th century Inca Empire)
Classical Nahuatl (lingua franca of 16th century central Mexico)
Classical K'iche' (language of 16th century Guatemala)
Classical Tupi (language of 16th to 18th centuries Brazil)
Classical Mapuche (language of 16th to 19th centuries Chile)
Early modern period
Renaissance Italian (language of the Italian Renaissance, 15th to 16th centuries)
Late Old Portuguese (language of Portuguese Golden Age, 15th to 16th centuries)
Early Modern Spanish (language of the Spanish Golden Age, 15th to 17th centuries)
Classical Azeri (lingua franca of the Caucasus Mountain region and language of Azeri literature, 15th to 18th centuries)
Classical Danish (lingua franca of the Kalmar Union and Denmark-Norway from the 15th to the 19th centuries and language of Danish literature from the 16th to the 19th centuries)
Old Lithuanian (the other language of the Grand Duchy of Lithuania, 16th to 17th centuries)
Early Modern English (language of KJV Bible and Shakespeare, 16th to 17th centuries)
Middle Polish (language of the Polish Golden Age, 16th to 18th centuries)
Classical Ottoman Turkish (language of poetry and administration of the Ottoman empire, 16th to 19th centuries)
Manchu language (language of the Manchus who ruled China, 16th-20th centuries)
Early Modern Dutch (language of the Dutch Golden Age, 17th century)
Early Modern French (language of France under Louis XIV, 17th to 18th centuries)
Classical Ladino (language of Sephardic Jewish literature, 17th to 19th centuries)
Classical Russian (language of the Russian Empire, 18th to 19th centuries)
Classical Mongolian language (the language of Mongolian literature and translations of Tibetan Buddhist religious texts from 1700-1900)
Classical Yiddish (language of the Yiddish Renaissance, 19th-20th centuries)
