How can I set the region in Terminal
The region is stored in ~/Library/Preferences/.GlobalPreferences, as the second part of the AppleLocale variable.  Some examples of the AppleLocale variable:


en_US system language set to English, region set to US
ja_JP system language set to Japanese, region set to Japan
en_DE system language set to English, region set to Germany


You can get more info from Apple's Developer Library, which also has links to the ISO 639-2 codes that can be used.