Add russian locale to debian

locale LANG

Edit /etc/default/locale and set the contents to:

LANG="ru_RU.UTF-8"

You can check which locales you currently have generated using:  

locale -a

You can generate more by editing /etc/locale.gen and uncommenting the lines for the locales that you want to enable. Then you can generate them by running:

locale-gen

You can find a list of supported locales in /usr/share/i18n/SUPPORTED