Even more technically, the line between dialect and language is a blurry one, decided in part by the speakers' intent and identity. British English, American English, Canadian English, Australian English, and Indian English are dialects, but Scots is its own language? Danish, Swedish, and Norweigan are separate languages, but Française French and Québécois French are dialects?

English speakers tend to have a very binary view of language vs. dialect, because English exists in this weird linguistic zone where its closest living relatives are all.. slightly different English. Sure, it can be a bit difficult to grok some terms from across the pond, but with a short list of vocab words you can generally understand other Englishes just fine, whereas you'll understand other languages pretty much not at all. There's not really any mutually-intelligible other languages that English speakers can more-or-less communicate with. At best, you can pick out a handful of similarities in germanic/scandi languages because of shared heritage.

That's not the case, globally. The Scandinavians (sans Finland) can all talk to each other, (the old running joke of sounds like drunk and/or with a potato in their mouth) but they're "different languages". Germans and the Dutch can generally understand each other, maybe not at full speaking speed, but at very least reading. A lot of African languages are essentially a spectrum of regional variants on each other, and so speakers of one will be able to make themselves understood to varying degrees to speakers of another depending on how far diverged they are; the same is largely true for the Middle East. But then we say Portugal and Brazil both speak Portugese; Spain and Mexico both speak Spanish. Even though there's quite the adjustment period for a person from one visiting the other.

There's no objective standard of what's "dialect" and what's "different language", but a large deciding factor is clearly national identity; people from different countries usually speak different languages (again, English is rather an outlier). The language spoken in Ukraine is not identical to standard Russian. They're at least as different from each other as some separate languages. So if Ukranians say they speak the Ukrainian language, not Ukrainian Russian, that's their call.

Oh my favorite: the political game of whether something is a dialect 🙄

Linguists generally take the position that Belarusian, Russian, and Ukrainian are partially mutually intelligible languages.

By what definition? Is it really mutual intelligible? I speak neither but from what I know, the pronunciation differs hugely and the vocabulary since Russian is influenced by Old Church Slavonic while Ukrainian has many loan words from Polish (which more often than not originate in Germanic languages).

Also: Someone smart once that a language is a dialect with a navi and an army and Ukraine has both, even though Putin would wish they didn't