Date (month) is displayed in english, even if locale is "de_DE"

Agenda & Cursus
8

It’s the placeholder for the date-range in both [[AgendaList]] and [[AgendaDetail]]: [[+range]]. All the lexicon fields get the right language. But for the range I get e.g.
25. May 2020, 10:00 – 17:00 Uhr – note that »Uhr« is correct!