Comment 9 for bug 1392699

By reading ubuntu-system-settings/trunk/plugins/language/language-plugin.cpp source code, it appears that this rather common problem (preferred en_US locale and 24-hour military clock) happens because selected language (translated to locale) is assigned *both* to the Language and FormatsLocale of the org.freedesktop.Accounts.User properties.

It can be fixed (until you change it with ubuntu-system-settings again) by changing FormatsLocale after you've set your desired language, and restarting device:

$ dbus-send --print-reply --system --dest=org.freedesktop.Accounts /org/freedesktop/Accounts/User$UID org.freedesktop.Accounts.User.SetFormatsLocale string:'ru_RU.UTF-8'