Are you only having problems because you don't know on the German system where the various settings are to change the language back to English?
If yes, here is what you would have to do:
Go to Einstellungen -> on the left choose Zeit und Sprache -> on the right use Sprache und Region, on the next screen you should see both languages, English and German. At the very top under Windows-Anzeigesprache choose English, then further down you want to change Land und Region to your country, and last change Regionales Format as well to whatever you had used before.