Hi there @Thomas_Roos , thanks for your post! Happy to clarify further 
Our date formatting in Asana is actually determined by your computer’s region setting. If your laptop or computer is configured for regions in a country that uses day/month/year, then your Asana instance will also appear as day/month/year, for example.
While it’s not possible to manually set the the display date format in Asana, it shows based on the language, and region sections of the browser and operating system the user accessing Asana from. Please note that If you’re using a VPN or other software that may interfere with how this is detected by Asana, the format may not change reliably.
There is a thread on our forum where other users have provided some tips on making changes to their browser or operating system that helped their different configurations that may be useful to read through.
Hope you find this information helpful