Hi Lukas B,
Please share which operating system are you using? Have you checked the operating systems region and languages settings?
I'm on OS X Mavericks and my system's language is german. Does my system-language affect the apps? Why is there an option called "App language" then?
Adjusting the Adobe Application Manager language is suppose to adjust the language of the applications. If for some reason it is failing to do so then please try removing the application in the following manner:
1.In the Finder, navigate to the Applications folder.
2.Drag the application to the Trash.
Please try reinstalling the other installed applications and from previous reports this will install the English language files.