Thank your for the provided information.
The "(blank)" string that is displayed when the header value is empty is not localized. It is hard-coded in one of the pivot engine's models. You can alter this behavior by defining a custom row and column header templates
where you can manually translate the "(blank)" string to the current language. You can see this approach demonstrated in the attached project.
Additionally, I've logged a feature request in the UI for WPF feedback portal
where you can track its status. And I also updated your Telerik points as a small gesture for bringing this to our attention.
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