The locale settings is not working with the v13.0 Date Picker. In 12.x and below, the "first day of the week" was controlled by the end user's "Account Settings" for Locale.
In v13, the Date Picker always displays "Monday" as the first day of the week. For end users who are used to their calendar being displayed with Sunday as the first day of the week, the new date picker is confusing.
In v12.x, the Date Picker was rendered as part of the UI XSL on the server; so Account Settings could be used as input into the date picker widget.
In v13.0, the Date Picker is part of a toolkit that we license from a third party vendor. The GXT date picker is rendered on the client (in the browser). This date picker always starts the week on Monday. That is how it was designed by the third party vendor.
Resolved in Clarity 13.1.0 Generic Patch. Reference TEC581256
Resolved in Clarity 13.2