What language do Ukrainians speak?

They speak Ukrainian

From the resources that I have found, the answer above is correct. You might also check out the information on the following link. Ukrainian language - Wikipedia, the free encyclopedia

What is quoted from it is below.

Quote:

---

Ukrainian (украї́нська мо́ва, ukrayins'ka mova, [ukrɑ'jinʲsʲkɑ ˈmɔʋɑ]) is a language of the East Slavic subgroup of the Slavic languages. It is the official state language of Ukraine. Written Ukrainian uses a Cyrillic alphabet. The language shares some vocabulary with the languages of the neighboring Slavic nations, most notably with Polish, Slovak in the West and Belarusan, Russian in the North and the East.
The Ukrainian language traces its origins to the Old Slavic language of early medieval state of Kievan Rus'. In its earlier stages it was called Ruthenian. "Ukrainian is a lineal descendant of the colloquial language used in Kievan Rus" (10th–13th century).[1]
The language has persisted despite several periods of bans and/or discouragement throughout centuries as it has always maintained a sufficient base among the people of Ukraine, its folklore songs, itinerant musicians, and prominent authors.

---