Hello Wudza,
I just checked your site (it looks very different now) and downloaded your .po file. I think I’ve found the issue. In the plurals setting (catalogue > settings), you use the following rule:
nplurals=3; plural=n%100/10==1 ? 2 : n%10==1 ? 0 : (n+9)%10>3 ? 2 : 1;
POEdit gives an error here, saying this is incorrect. I also noticed that you have three times the same translation for this word. The default for Russian is:
nplurals=3; plural=(n%10==1 && n%100!=11 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2);
Something else I found is that you did not use the %d in the translation, but this is absolutely necessary – it stands for the number that is inserted there!
On a final note, you are using WooCommerce Menu Cart but you’re posting here to the WP Menu Cart forum. WP Menu Cart is the best of the two (also for WooCommerce), and it includes Russion translations by default.
Let us know if you have any questions!