https://www.wikidata.org/wiki/Q35499
medieval Slavic literary language, without ISO codes, preceding Church Slavonic (Q33251, cu, chu)
old church slavonicwikidata
https://www.omniglot.com/writing/ocslavonic.htm
Old Church Slavonic is the old literary language of the Slavs and the liturgical language of the Easter Orthodox Church.
old church slavonicalphabetlanguage