It is really only in European countries where Germanic languages (German, Dutch, English, ...) are spoken, that the A-G or A-H letter system is common. Other countries, including Russia and I assume also Ukraine, use fixed-do solmization in formal music education.
I see a lot of sources online where Russian or Ukrainian is mixed with Latin-script note names, so it's possible that Ukrainians will recognize "do, re mi, ...". Sources that use Cyrillic script have these names, which seem to be phonetic versions of French solmization:
flat бемоль (bémol)
sharp диез (dièse)
So a key or chord would be named e.g. "фа-диез минор" (see Wikipedia). I don't know whether there is a standard way of simplifying or abbreviating these.
Younger people may of course have watched English or German-language music lessons on YouTube, or looked for sheet music or tabs online, and may be familiar with "Em" and "F#" and "Bsus4".