I just installed a new Plone 5.2 site with the Universal installer.
When I use the DateTimewidget for the default Event, is uses 'english format.'
How can I fix this?
PS: The browser views shows the data correctly ( 19.00 instead of 7pm)
...depends on the choosen site language. Dates for DE/German are in 24h format.
I use Norwegian, which is also in 24h.
In fact, I changed to German/DE but I still have the same.
Is this a setting in buildout (and not in Plone itself ?)
No, I changed it in the Language control panel
Oh yeah, in German it shows 17:27.
I'm in French and I see 5:27 p.m. in this widget instead of 17:27
Where it is configured that for a given language it should be 24h?
isn't that configure somehow through the locales?
I dont know if this is related, but I noticed that the text too is in English.
(in my po-file I have entries for both 'select date' and 'select time', but only 'date' is translated
I replied to myself in https://github.com/plone/Products.CMFPlone/issues/3134
for German, we have the following translation in plone.app.locales/plone/app/locales/locales/de/LC_MESSAGES/plone.po
#. Default: "h:i a"
#: plone.app.widgets/plone/app/widgets/utils.py:72
msgid "pickadate_time_format"
msgstr "HH:i"
Are you in buildout.coredev 5.2 ? plone.app.locales is always in auto-checkout. You need to restart the instance to build the mo file from the po file. I just did the change for French, looks great. 
Added a new site and it works
For reasons I have to find out later, the 'Select time' still shows in English
Now I just wish it 'started on 12.00 (not 00:00 where one has to scroll 12+ hours forward)
UPDATE; It looks like 'Event Start and End time' behaves slightly different than 'Publication date (even for the same object), so I only see 'Enter time' for Publication date, since start and end time is automatically selected to 'almost current time' (?)