Steps to reproduce:

1. System language "Russian"
2. Create user "Test" with language Portugal
3. Open another browser, on chrome in incognito mode. 
4. in one browser login as "Admin" in another as "Test"
5. As Admin, disable "Test" user.
6. As "Test" user, press on any menu, and accept warning message. Login page in russian language.
7. As Admin - enable "Test" user. 
8. As "Test" user press login button (without adding credentials). 

Result:
Login page language changed to Portugal. 

Expected:
Login page language is in Russian language.