Joseph S. answered 07/31/19
Focused Tutor in English & Russian (Novice to Advanced Levels)
Most people in Ukraine speak Ukrainian, which is an East Slavic language that is closely related to Russian and Belarusian. Roughly two-thirds of Ukrainians consider Ukrainian to be their native language. It is also the official language of Ukraine.
However, Ukraine is very closely connected to Russia historically. It was a part of the Soviet Union for many years, with Russian being the primary language of Ukraine for most of that time. As a result, many people in Ukraine speak Russian as well as Ukrainian. About one-quarter of Ukraine's population considers Russian to be their native language.
It is not uncommon for Ukrainians to mix the two languages and speak what is called "surzhyk." There is no set of rules for such a hybrid language, it is simply non-standard Ukrainian and/or Russian. There are also a wide array of minority languages spoken by indigenous and immigrant populations.