Localization of AngularJs date filter in embedded forms

I successfully added German localization to the Camunda apps (tasklist, cockpit etc.) via configuration.
This in a shared process engine environment.
The labels are translated as expected to German, but I have a problem with the date format.
On my embedded forms, I show dates using AngularJs syntax. e. g.

<th scope="row">Rechnungsdatum</th>
<td>{{rechnung.rechnungsDatum  | date : 'medium'}}</td>

This works but the date is shown in English using US Locale and not German as expected.

How do I have to configure the system so that I also see the date in the expected German localization?

Thanks
Dario