Hi Alexander,
See the notes at the bottom of our localization page, you should not change that setting, it should remain as auto:en-US because only the English resource files have no missing keys and if you set it to another language and there are missing keys it can throw null reference exceptions.
Instead you should set the site default culture like this in user.config
<add key="UseCultureOverride" value="true" />
<add key="site1culture" value="ru-RU" />
Note that if you have a multi site installation you must make a setting for each site:
<add key="site2culture" value="ru-RU" />
<add key="site3culture" value="ru-RU" />
...
This way it will use Russian but it can still fall back to English resource strings if the key is missing in the Russian resource file.
Hope it helps,
Joe