To change the Language for a Office 365 mailbox (Exchange Online), run the following commands:
$O365Session = New-PSSession –ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell -Credential $O365Cred -Authentication Basic -AllowRedirection
Import-PSSession $O365Session
Set-MailboxRegionalConfiguration -Identity “USER” -Language nb-no -LocalizeDefaultFolderName
For full list of cultureinfo classes (Languages) see:
https://msdn.microsoft.com/en-us/library/system.globalization.cultureinfo(VS.71).aspx
