If I want to set the regional configuration of newly created or migrated mailboxes, is the following ScriptingAgentConfig correct? 

<?xml version="1.0" encoding="utf-8" ?>
<Configuration version="1.0">
<Feature Name="Mailboxes" Cmdlets="New-Mailbox, Enable-Mailbox, New-MoveRequest, Resume-MoveRequest">
<ApiCall Name="OnComplete">
if($succeeded) {
$Name= $ProvisioningHandler.UserSpecifiedParameters["Name"]
Set-MailboxRegionalConfiguration $Name -Language en-us -DateFormat "M/d/yyyy" -TimeFormat "H:mm" -TimeZone "China Standard Time"
}
</ApiCall>
</Feature>
</Configuration>

Hi 

Your agent looks fine 

Just add -DomainController $DC.domain.comas well

Hi,

Great advice from Sathish.

Since this issue is related to script of Exchange server. I recommend you to contact Scripting for Exchange Server Team so that you can get more professional suggestion, please refer to: https://technet.microsoft.com/en-us/scriptcenter/dd742246.aspx?f=255&MSPPError=-2147217396