A sacred language is a language, frequently a dead language, that is cultivated for religious reasons by people who speak another language in their daily life. In particular, a liturgical language is a sacred language.

The traditions involved in religious ritual and liturgy quite frequently provide a place where archaic forms of language occur. One of the last places the obsolescent English pronoun thou remains in frequent use is in religious liturgy; wherever the Authorised Version of the Bible is read, or older versions of the Anglican Book of Common Prayer are in use.

The use of a sacred language represents a further development of this practice. Here, language has changed so far from the language of the sacred texts that the language of the old liturgy is no longer comprehensible without special training. Missionary and pilgrim faiths may then spread the old language to populations which never spoke it, and to whom it is yet another foreign language. Once a language becomes associated with religious worship, its believers often ascribe virtues to the language of worship that they would not give to their native tongues. The sacred language is typically vested with a solemnity and dignity that speech in the vernacular lacks. The enterprise of training clergy to use and understand the sacred language becomes an important cultural investment. Their use of the tongue gives them access to a body of knowledge that untrained lay people cannot access.

A number of languages have been used as sacred languages. They include: