Russian language
Russian (ру́сский язы́к, russkiy yazyk, pronounced [ˈruskʲɪj jɪˈzɨk] ( listen)) is an East Slavic language and an official language in Russia, Belarus, Kazakhstan, Kyrgyzstan and many minor or unrecognised territories. It is an unofficial but widely-spoken language in Ukraine, Latvia, Estonia, and to a lesser extent, the other countries that were once constituent republics of the Soviet Union and former participants of the Eastern Bloc. Russian belongs to the family of Indo-European languages and is one of the three living members of the East Slavic languages. Written examples of Old East Slavonic are attested from the 10th century onwards.

Q: What language sub-family is Russian in?
East Slavic