Is it possible to launch a program in a specific language?
You can change the language inside the preferences file of the application :

defaults write com.apple.TextEdit AppleLanguages '("en-US")'


Or just run once one application with another language :

/Applications/iCal.app/Contents/MacOS/iCal -AppleLanguages '(de)'




To determine the bundle identifier, run

mdls -name kMDItemCFBundleIdentifier /Applications/Mail.app


or directly in one command:

defaults write $(mdls -name kMDItemCFBundleIdentifier -raw /Applications/Mail.app) AppleLanguages '("en-UK")'


(via SuperUser)