Cyril and Methodius were brothers born in Thessalonica, Greece. They were sent by the Byzantine Emperor to evangelize the Slavic people. In the course of their work they created a written language, inventing the Cyrillic alphabet for it, and translated the Bible and the liturgy.
Pfatteicher in "Festivals and Commemorations: Handbook to the Calendar in Lutheran Book of Worship" says:
-"The Slovaks, Czechs, Croats, Serbs, and Bulgars all revere the memory of Cyril and Methodius as founders of their alphabet translators of their liturgy, and builders of the foundation of their literature as well as heralds of thegospel in their land"But what I find interesting and timely about these two is that their efforts at translating the Gospel and liturgy into the language of a people who had no familiarity with Latin or Greek was met with opposition, particularly among the Western clerics. Even though Cyril got his translations approved by the pope, he died soon after that and Methodius was still met with opposition, sometimes violent. Apparently to some of these folks only the languages written on Pilate's sign on Christ's cross --Greek, Latin and Hebrew-- could authentically convey the truth of Christianity.
The Gospel spread the way it did when evangelists were able to separate the Gospel from the culture and find a way to proclaim the Good News of God's forgiveness and new life in Christ to all people in all languages. This is the promise of Pentecost – when visitors in Jerusalem from all over the world heard the good news in their language. That is the role of the preacher – to speak the Good News in language people understand.