You'd have to install the English language pack from System -> Administration -> Languages. Then log out and log in again but on the GDM screen choose English for the language in the Options menu.
I attached a screenshot to show what I mean by "middle part." There's the Model section where you choose MacBook. Then there's the Selected Layouts part. That's what I meant by "middle part." Is German/Deutsch listed there? If not, add it by using the Add button just below there. It'll bring up a new window, and you can pick Germany/Deutschland from the top drop-down. Just below that you can pick the specific layout. Hit Add at the bottom of that window, then click and drag German/Deutsch from the list in the "Selected layouts" and move it to the top of the list and make it default.
You'd have to install the English language pack from System -> Administration -> Languages. Then log out and log in again but on the GDM screen choose English for the language in the Options menu.
I attached a screenshot to show what I mean by "middle part." There's the Model section where you choose MacBook. Then there's the Selected Layouts part. That's what I meant by "middle part." Is German/Deutsch listed there? If not, add it by using the Add button just below there. It'll bring up a new window, and you can pick Germany/Deutschland from the top drop-down. Just below that you can pick the specific layout. Hit Add at the bottom of that window, then click and drag German/Deutsch from the list in the "Selected layouts" and move it to the top of the list and make it default.
Does that work?