Thank you for bringing this issues to us.
a) The translation issues in the backend you announced are logged and we are grateful for your insight.
b) The message is aimed to translate Publish/Unpublish and in my little knowledge of German "Aufhebung der Veröffentlichung planen" is "Repeal of the publication plan" and "Veröffentlichung planen" which is Publication schedule is not very similar to Unpublish.
c) There is a check to see if the unpublish date is not in the past ( see screenshot ). What is your scenario on making it allow an old date?
All the best,
the Telerik team
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