GUI Translation update for 6.1 release

[Torsten Lilge]

Dear Translators,

I have once again updated the translation files (libgui/languages/*.ts)
of the GUI for the 6.1.0 release (and completed the German translation).
This was necessary do to some translation issues that were uncovered
during the first translation and due to a recent changeset adding a new
feature which should bw included in the new release.

I would like to ask those who have already finished the translation
(thank you very much for that) to just finish the few additional new
strings.

Those who are already working on the translation based on the old
language files, please just send me the completed files or upload them
to bug report https://savannah.gnu.org/bugs/index.php?57490, I will
merge them with the current changes.

If you have not yet started to translate the file entries, please just
take the file in its current version.

In any case, please mark already translated entries as "finished" if
there are no more questions or ambiguities regarding this entry.

Thank you very much,
Torsten