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

Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
[DRAFT] l10n: de.po: translate 24 new messages

Translate 24 new messages came from git.pot update in 2dcc7d2
(l10n: git.pot: proposed updates for v2.0.0 (+24)).

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