This issue is caused by wrong translations. In Russian the “one” key isn’t only used for the value 1, but also for 21, 31, 41,… That’s why you should always use %{count} instead of the value “1” within translations, otherwise all those values will be truncated to 1. 
So, you’ll need to update all pluralized strings and make sure that the “one” key contains the appropriate count variable instead of the value 1. You can use the “pluralized: yes” filter on Transifex to find all the affected strings.
As an aside, the plural rules used by Discourse aren’t 100% correct. According to the Unicode Plural Rules there should be “one”, “few”, “many” and “other”.
“many” was removed in 2014, because there was an issue with Transifex, which seems to be fixed since 2015. We never added it back and looking at the plural rules I think it doesn’t matter a lot, because I believe we aren’t displaying decimal numbers anywhere in the UI. But please be aware that Discourse is currently using “other” where it should be using “many”!