German translation: translated assertion-/exception-like strings

Change-Id: I5146951c6a1e569f7c7b36fc734c1c69f0b994f3
Reviewed-on: https://gerrit.libreoffice.org/7598
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>