The Byzantine Catholic Churches and the non-Byzantine Churches in union with Rome use the same liturgies as their Orthodox brothers and sisters.  Union with Rome does not mean giving up one's liturgical practices or accepting  the western liturgies. Pope John VIII in 879 approved the use of the vernacular Slavonic language for use in the mass (divine liturgy)  in areas converted by Sts. Cyril and Methodius and said "Nor is it in any wise opposed to wholesome doctrine and faith to say Mass in that same Slavonic language (Nec sanæ fidei vel doctrinæ aliquid obstat missam in eadem slavonica lingua canere), or to chant the holy gospels or divine lessons from the Old and New Testaments duly translated and interpreted therein, or the other parts of the divine office: for He who created the three principal languages, Hebrew, Greek, and Latin, also made the others for His praise and glory (Boczek, Codex, tom. I, pp. 43-44).