It's actually really easy, but you need to speak Ukrainian, or Russian. And some Ukrainians speak both.
On the other hand, Official Ukrainian documents are in Ukrainian since that is the official language. A simple example will give you an idea of the difference. This is "you are welcome". The phrase on the top is Ukrainian and the bottom is Russian.
Нема за що! (Nema za shcho!)
Не за что! (Ne za chto!)
Now, one way that people who have shown that the documents saying there are Biolabs are fake is that the documents produced to demonstrate that are in Russian. The difference is like that between Swedish and Danish: someone who isn't familiar will not notice too much of a difference. But someone who knows the languages will spot them immediately.[1]
Also, machine translators will "burp" if you can get a transcription of the document and try and translate it in the wrong language. Parts will be total jibberish if it isn't translated correctly.
As I have mentioned in a couple of posts: Ukrainian is closer to Polish than Russian. The major difference between Polish and Ukrainian is the alphabet. Russian is different from Ukrainian.
So, yeah, I believe someone when they tell me the documents are fake: especially when the ones they show me are written in Russian!
And people in the US think these clowns could mess up their elections.
паляниця, і до побачення !
Footnote:
[1] I know this from watching Nordic Noir.