https://www.russiantutoring.com/post/wh ... ow-russian
Russian belongs to the East Slavic branch of the Slavic subfamily of the Indo-European family of languages. If you speak Russian, it will be easier for you to understand other Slavic languages, which include Ukrainian, Belorussian, Polish, Czech, Slovak, Bulgarian, Serbian, Croatian, Bosnian, and Slovene.
Ukrainian and Belarusian are the closest languages, as together with Russian they form the East Slavic group of languages. These three languages have an 86% lexical similarity; that is, they share 86% of the same words.
If you can speak Russian fluently, you will be able to understand 77% of Polish words, while Czech, Slovak, Bulgarian, and Slovene have a 74% similarity to Russian in terms of vocabulary, which decreases to 71% for Serbian.
My husband grew up speaking Czech in a small town in Iowa. He once told me that Russian was pretty similar to Czech. My dad, a small town doctor in the '50s and '60s, made house calls in rural Wisconsin and learned certain Polish terms in order to communicate with the outlying farmers. He shared those words with my sweetie who could understand them. The word for
pain, for example, was almost identical in Czech and Polish.
Edited to add - It looks like the Russian word for
pain is similar. In Czech, it sounds like bolie.