In my Plone 4.2 site the DatePicker (e.g. when adding a new “event”) displays as YEAR MONTH DAY

However, I do have a German Website, where it should be the other way around. That is:
DAY MONTH YEAR. How can I change this?
PS German is already selected as default language from Plone’s language control panel.
PPS I don’t know if this is related in any way, but since this might be a localisation issue, I’d rather tell: I use raptus.multilanguageplone
edit: added correct image link | say, that this happens when adding/editing a new event
I can’t see the image you added because the URL is expired. so I’m going to assume you mean for the add/edit form of an Archetype (In Plone 4.2 the default types are all Archetypes).
There seems to be no easy fix such as a site-wide setting in the control panel, but you can change the ordering in the calendar_macros.pt template. This however means you’ll have to change the raw HTML.
To do this, you’ll have to go to the Zope Management Interface (reached via the Site Setup page “Plone/@@overview-controlpanel”).
Then click on the “portal_skins tool” and then “plone_templates”. Then click on “calendar_macros” and then click the “Customize” button.
Now you can change the ordering in the raw HTML/TAL.