Thread:Support/Where is time stamp message for Echo extension?

I search for the time stamp message that displays the notification date in the Echo window on the top of a wikipage, see the image below:

Screenshot

This is in Upper Sorbian WP but the time stamp is shown in the fallback language German (inside the red ellipsis). I need the name of the message to translate it into Sorbian.

I didn't find that message among the messages of the Echo extension on translatewiki.net.

Thanks in advance and kind regards,