l10n: de.po: prepare de.po for new round of translation

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
l10n: de.po: translate 27 new messages

Translate 27 new messages came from git.pot update in
df49095 (l10n: git.pot: v1.9 round 1 (27 new, 11 removed).

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>