The most common language in the nation of Yugoslavia is called Serbo-Croatian. But people in Yugoslavia use two different alphabets to write the same language. One alphabet is the Roman, the one we use; the other is called the Cyrillic, and is the same alphabet as the one used in Russia.
During the 9th century, a missionary named Cyril taught Christianity to Slavic people in Eastern Europe. But these people had no written language. So, in order to teach them to read the Bible, Cyril invented an alphabet based on the Greek alphabet.
Serbians in Yugoslavia still use this alphabet, the Cyrillic, to write Serbo-Croatian. But the, Croatians who were taught Christianity by missionaries who wrote with the Roman alphabet use the Roman alphabet today to write Serbo-Croation!
There are today about 65 different alphabets in use around the world!