What decides the Content-Language in Internet headers of Outlook?

[rabau]

Hi Everyone,
I found weird that any mail generated by outlook will have message"Content-Language ",
Which is explained by Microsoft that it's by your default languages set in your Office (File-> Options -> Language -> Choosing Editing Languages)
Whatever Languages I choose here has no effect to the "Content-Language" internet Header.


Also I tried to Install other languages pack, no changes.

But If I sent e-mail from my friend's PC which has both Windows 7& Office 2013 in French, the internet header is "Content-Language: FR"




I don't understand, anyone's help will be very appreciated.