Languagesetup

To configure the language that OS X uses at the login window, you can use the "languagesetup" command.

The man page for language setup leaves a lot to desire, but if you run "sudo languagesetup" with a bad flag, or the -h flag, it gives you some more information:,

 $ sudo languagesetup -h
 Usage:	languagesetup [-h] | [-Localized|-English] | [-langspec <spec>]
 	-h		print this message
 	-Localized	print localized prompts (requires UTF8-capable terminal)
 	-English	print English prompts (default through 10.3)
 	-langspec	specify a language directly (eg. "English" or "ko")

To set the language using the command line in a first boot script, you first need to know how to specify the language that you need. Using the following command you can get a list of the languages. The language identifier is printed in quotes.

 sudo languagesetup -English

Using the identifier in the quotes, you can set the language to what you need:

 sudo languagesetup -langspec "English" #Set language to English

Or for Spanish:

 sudo languagesetup -langspec "Spanish" #Set language to Spanish

Apple KBase Article:http://support.apple.com/kb/HT4102