How do I change the language via a terminal?

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http://askubuntu.com – Using system settings I changed my language to Arabic and deleted the English language from the settings. Then the computer lagged and it logged out - now I can't log back in because the login is in Arabic. So is there a way to default my language via terminal, default the login password language, or login via terminal which is still in English. I only have access to guest and a terminal. (HowTos)