Hi Joachim,
The best place to edit your language preference is from your User Profile dropdown menu (on the top right of your screen).
From there, click User Profile. Then click the Edit (pencil) icon in the bottom right:
Next, you will edit the Language field, using the drop down menu to select English. Save your changes by clicking the green check mark in the bottom right corner.
You can find more information about personalization in our blog article here: SAP ONE Support Launchpad: Personalization
I hope this was helpful for you. If not, please let me know and I'd be happy to investigate further.
Best Regards,
Jamie