Isolinux sets the keyboard layout depending on the selected language instead of the selected keyboard, but its set the correct keymap.
Try to detect a correct xkb layout using the keymap, and if its fails use the xkblayout that isolinux provides in the cmdline.
Setup x11 config file in the CLI installer
Move the keyboardctl fix to _write_x11_config_file() so the installer also works with keyboardctl
Fixes