Text has been mangled, so lets speek by pointers:

The translation on line 93 in file

/usr/lib/GNUstep/SOGo/SchedulerUI.SOGo/Resources/Russian.lproj/Localizable.strings

should read as translation on line 265 in the same file.

Also, I would suggest keep only firt word of translation ("Confidential") as long translation ("Confidential event") doesn't fit and wraps to label of "Privat event"

Could you please create an account on Transifex and commit the changes yourself?

See http://www.sogo.nu/english/nc/support/faq/article/how-to-translate-sogo-in-another-language.html

Thanks!

Ok, request to join Russian team is sent

Done

Translation updated on Transifex - it'll be updated for the release.