Translate German DBG_ASSERT() message to English.

Change-Id: I647d55c2b64ab3ea8b33a132e998ed023d91f000
Reviewed-on: https://gerrit.libreoffice.org/7497
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>