I’m not sure if you can change the date formatting for the calendar layout. I think it’s pre-set base on your locale. I’m guessing this particular translation makes it longer than some other languages. I only say that because the calendar is pretty smart in being able to recognize almost anything remotely resembling a date, even if it’s not recognized as a date format in the data editor. It’s very forgiving.
@darder you could consider creating your own calendar with a cards layout and grouping instead.