Mac OS X Hints: Set the language for a single application

defaults write com.microsoft.Excel AppleLanguages '("ru-RU")'
defaults write com.microsoft.Word AppleLanguages '("ru-RU")'
defaults write com.microsoft.Powerpoint AppleLanguages '("ru-RU")'

defaults write com.apple.iTunes AppleLanguages '("ru-RU")'
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
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