The line under the user's nickname indicates how long the account already exists. Different languages may need to use different cases for this. We need to come up with a solution to how this can be done.
For the Russian language, this may be related to the following task: T257500: Grammatical cases for site name for ruwiki
Thread started here: https://www.mediawiki.org/wiki/Topic:Vsv66lgc9jt1ka5n
Also see: T258188: [[MediaWiki:Growthexperiments-homepage-startediting-dialog-difficulty-subheader]] translation issue: use grammar template