German you haven't set up modules, menus and templates for Russian language properly. To make this work do this:
0. Make sure you have installed Russian language in content languages
1. Duplicate template and in settings of it make it default for Russian language
2. Create Main menu and assign default page for Russian language
3. Go to template settings and in menu settings select menu you have created for Russian language
4. Assign modules for russian pages
5. MOD_LOGIN_ME SIGN_UP strings are displayed because you need to make language overrides, just open overrides for English version and make ones for Rusian
Thats all you need to do.
Here is complete manual from Joomla if you need it:
docs.joomla.org/J3.x:Setup_a_Multilingual_Site
docs.joomla.org/J3.x:Setup_a_Multilingual_Site/Creating_menus
Regards from Serbia