Slavs
Slavs are the largest ethno-linguistic group in Europe. Present-day Slavic people are classified into East Slavs (chiefly Belarusians, Russians, Rusyns, and Ukrainians), West Slavs (chiefly Czechs, Kashubs, Moravians, Poles, Silesians, Slovaks and Sorbs), and South Slavs (chiefly Bosniaks, Bulgarians, Croats, Macedonians, Gorani, Pomaks, Montenegrins, Serbs and Slovenes).
Ukrainian language
Some researchers, while admitting the differences between the dialects spoken by East Slavic tribes in the 10th and 11th centuries, still consider them as "regional manifestations of a common language" (see, for instance, the article by Vasyl Nimchuk). In contrast, Ahatanhel Krymsky and Alexei Shakhmatov assumed the existence of the common spoken language of Eastern Slavs only in prehistoric times. According to their point of view, the diversification of the Old East Slavic language took place in the 8th or early 9th century.