The Russian language belongs to the Indo-European language family. It is included to Slavonic group. It has many relative languages. Ukrainian, Belarusian, Bulgarian, Polish, Serbian are among them. These languages have much in common. Russians easily understand Belarusian and Ukrainian and also conversely. The others are harder to understand. Though they are connected with pronunciation and accent in some way. If you were to write down phrases, for example, in Bulgarian then it will be possible to see more in common with its Russian equivalent.
“The Russian language is great and mighty” – wrote Lev Tolstoy (Leo Tolstoy). That is the first thing that comes into the head of a Russian when they talk about their native language.