It's a double holiday today, Eid al-Fitr and the day we celebrate the Cyrillic alphabet in Bulgaria, which is also used by millions of Muslims around the world. So Eid Mubarak and Happy May 24th!
عيد مبارك!
Честит празник!

Dedicating a special day to celebrating the creation of the Cyrillic alphabet shows the importance given to literacy in Bulgarian history/culture which is closely associated with the idea of "enlightenment" - not that different from how Islam sees and celebrates literacy.

The creation of the Cyrillic alphabet is seen as empowering cultural production and prosperity among Slavic people as prior to it, most Slavic tribes used rudimentary scripts/writing systems. It also allowed the translation of books written in Latin/Greek, including the Bible.

The two men we celebrate on May 24, Cyril and Methodius, laid the foundations of the Cyrillic script, but did not create it. They instead created the Glagolitsa which had a short life-span due to its complexity and was first used in Great Moravia (present-day Central Europe)

Their pupils, who were eventually kicked out of Moravia, made their way to Bulgaria, where Czar Simeon commissioned from them a new script, which eventually was named Cyrillic, in honour of Cyril. The man most credited with the creation of this script is Clement of Ohrid.

And just to clarify - Cyril and Methodius were not Bulgarian, nor Russian, nor Macedonian, as some may claim. They were born in Thessaloniki, in the Byzantine Empire, and most likely had the identity of Byzantine subjects, not a modern-day ethnic identity.

They may have had a Slavic mom and knowledge of Slavic may have helped in their task - create an alphabet to facilitate the spread of Christianity among the pagan Slavs and encourage them to choose Constantinople over Rome as a religious/political reference.

One last fun fact: when the subjects of Kievan Rus converted starting 988, guess who helped out with the literacy part...Bulgarians, which may explain why I have an easier time with Church Slavonic and old Russian than with present-day Russian street slang.