I hate Excel for Mac.

They did localization also to the function name! Think about you’re writing a Javascript program in Italiano:

per(var i = 0; i < amici.lunghezza; i++)

Fortunately, today I just found how to change it back to English (also for other applications)

$ defaults write com.microsoft.Excel AppleLanguages '("en-US")'
$ defaults write com.microsoft.Word AppleLanguages '("en-US")'
$ defaults write com.microsoft.Powerpoint AppleLanguages '("en-US")'

Now the Office for Mac is great again!