ok, I figured it out on my own (the keyboard-layout-issure), maybe it’s helpful for someone else as well:
as the OS is arch-linux, the file /etc/X11/xorg.conf.d/20-keyboard.conf has to be created and should contain (for instance in case of a german-language-keyboard) the following:
Section "InputClass"
Identifier "keyboard"
MatchIsKeyboard "yes"
Option “XkbLayout” "de"
Option “XkbVariant” "nodeadkeys"
EndSection
and as the filesystem is mounted read-only you first have to remount it:
mount / -o remount,rw
(as it can be found here _> Using a wifi adapter)