[Koha] Onboarding not working for language de-DE

[zefanja]

Hello,

when I try to proceed with the onboarding process after the installation 
I get this error:

Template process failed: file error - 
/usr/share/koha/intranet/htdocs/intranet-tmpl/prog/de-DE/modules/onboarding/onboardingstep1.tt: 
not found at /usr/share/koha/lib/C4/Templates.pm line 122.

I've set the language to de-DE.

Ubuntu 20.04, Koha 20.05 (lastest from stable channel)

Any ideas? How can I reset the language to finish the onboarding? Or do 
I have to start again?

Regards,
Stephan