One/many plural rule for Russian/Belarusian/etc
The plural selector variable within the expression {{...}} is not inserted into the resulting expression. If a numeric expression is required, the variable is used again outside of the expression. Thus {{plural:%number%|one=Horse|other=Horses|default=Horses}} is expanded to "Horse" if %number% is one, and to "Horses" otherwise. The "default" rule is used when no %number% is supplied at all. So, I think the distinction between "other" and "default" is exactly what you are looking for.
Hello Burschik, thank you for your reply.
Hm, but the result view that appears after translation uses the other rule. The result of the translation is other=tkalčich mištrow if I use other rule for numbers resp. other=tkalči mištrojo if I use the other rule for missing numbers. Until now I used the nominative singular for the default rule but in the result view after translation displays the other rule.