Adds settings for disabling browser language detection and language preference (#2691).

git-svn-id: http://svn.redmine.org/redmine/trunk@12691 e93f8b46-1217-0410-a6f0-8f06a7374b81
Adds locales strings (#2691).

git-svn-id: http://svn.redmine.org/redmine/trunk@12692 e93f8b46-1217-0410-a6f0-8f06a7374b81