l10n: de.po: translate 4 new messages

Translate 4 new messages came from git.pot update in 28e1aaa (l10n:
git.pot: v2.13.0 round 2 (4 new, 7 removed)).

Signed-off-by: Ralf Thielow <[email protected]>
Acked-by: Matthias Rüster <[email protected]>

Author: ralfth