2014-10-11 OS X
By default, login window language will be set to the same language that you have chosen during instalation of your OS X.
If you want to change it, you will need just terminal and administrator privileges. Open terminal (if you don’t know where it is, type ⌘ Space to open Spotlight – then type “terminal”).
Use below command:
Type administrator’s password when prompted and then pick a number next to language you want to choose.
Confirm by pressing return. That’s it.