One possible solution that I could think of is to check the resource of the Appointment object in the Page_Load event of the AdvancedForm code behind and load the data accordingly as it is done in the sample you linked:
sender, EventArgs e)
(ContinentsRadComboBox.Items.Count == 0)
// Check the resourse and fill the continents of the combo
Hope this will be helpful.
the Telerik team
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