Proper format of PreferredLanguage AD attribute

Question

I'm trying to resolve an Office 365 issue related to languages. In a support article, https://community.office365.com/en-us/f/148/t/205002, is says the preferredLanguage attribute should be set when using dirsync to populate your O365 tenant. This is not set in our AD currently. What is the proper format of this field?

I've tried en-us, and this does not seem to work. I have seen other references that it should be US English. Is there a reference somewhere that depicts what the options are or what the format for this AD attribute?

Solution

So after talking with support, the preferred language attribute would follow the language culture name format, en-US.

https://msdn.microsoft.com/en-us/library/ee825488(v=cs.20).aspx