Russian is an Alfresco supported language pack, so it's included out of the box and you don't need to download anything extra to get it installed.
Share and the repository have different language settings. The repo picks its language up from the system language when you start it up - it sounds like that is correctly detecting the system language as Russian.
Share, on the other hand, uses the browser's Accept Language header to determine what language the user is requesting the Share interface in - this varies from user to user, so each user needs to configure their system according to their individual language preference. It sounds like this might be where your problem is. There is information on the browser specific configuration on the W3C site, hopefully that will enable you to correctly view Share in Russian: Setting language preferences in a browser
Hope that helps,
David.
