What is the main language of Eastern European countries? Can a friend who knows something tell me?

Ukraine, Estonia, Latvia, Lithuania, Belarus, Poland, Hungary, Romania, Bulgaria, Georgia and Russia are mostly Slavs.

Slavic language family

Slavic language family is a language family of Indo-European language family. It was founded by the Byzantine priest Cyril and his brother Mitodi when they preached among Slavs in Eastern Europe. It can be divided into Eastern Slavic branch, Yugoslav branch and Western Slavic branch. The Eastern Slavic branch and the Yugoslav branch use Cyrillic letters, but with one exception, Serbian and Croatian are the same language. For religious reasons, Serbian is written in Cyrillic alphabet, Croatian is written in Latin alphabet, and the two letters can be transliterated freely. Slovenian is written in Latin letters. The West Slavic language family uses Latin letters. The languages represented by each branch are as follows: Slavic family >; Eastern Branch = Russia \ Ukraine \ Belarus