West Slavic languages
Due to heavy borrowings from Polish, German, Czech and Latin, early modern vernacular Ukrainian ("prosta mova", "simple speech") had more lexical similarity with West Slavic languages than with Russian or Church Slavonic. By the mid-17th century, the linguistic divergence between the Ukrainian and Russian languages had become so significant that there was a need for translators during negotiations for the Treaty of Pereyaslav, between Bohdan Khmelnytsky, head of the Zaporozhian Host, and the Russian state.