Recovering after interrupted Update fails: chroot: failed to run command '/bin/bash': Input/output error

New problem, but I will stay within this thread for now, if its ok.

Many programs (eg thunar) need very long to start up.
I know, that there was this problem in the past and a work around: [Stable Update] 2023-06-04 - Kernels, Gnome 44.1, Plasma 5.27.5, Python 3.11, Toolchain, Firefox - #2 by philm

So I tried to do the steps and ran into another problem:
The User-Password includes a german Umlaut (aöü). When entering the user password for login, it works fine. But in the terminal, It does not accept the password. In the terminal settings, unter advanced, the “default character encoding” was set to Default (ANSI_X3.4-1968). Changing it to something like UTF8 enables me to type Umlaute when entering a command, but the password is still not accepted.
I found that in /etc/locale.gen de_de needs to be uncommented, but to change this, i would need to enter sudo, which I cant…
In Manjaro-Settingsmanager, everything is i German and de_DE.UTF-8 is selected for everything). But the Program Names and everything in the regular settings is in english (was it before? not sure…)
Any ideas?