Thank you but thats not it, it is correctly set in WordPress. I also have a booking plugin that show the date in the wrong way. I feel it has something to do with the locale setting on the server, I change it to french but maybe I forgot something?

WordPress, from what I know, does not pull any date formatting from the system. The onlythings that can modify that are themes and plugins.

I want to assume your theme or plugin has the date format hardcoded into it because normal WordPress themes and plugins ask WordPress how to format it. So if it is not doing that, you will need to edit the theme and/or plugins to make them either formatted the way you want or use the functions the_date() and the_time() to pull them from the WordPress settings.

More information here

Did you check your date.timezone settings on PHP?

php.ini
----------
date.timezone = "US/Central"