Weaver II and Weaver Xtreme include German translations, and when properly installed (WP installed with de_DE), then Weaver should show all visitor side messages in German.
(the admin side messages are not translated)
Note that the first search-results you changed is in an HTML class, and should never be touched. The second is wrapped in the __(‘english’,’weaver-ii’) translation call (the __), which should mean that the phrase should show as “Suchergebnisse für:” already. That phrase is definitely included in the Weaver II translation files.
So, if you aren’t seeing that, there is something faulty about your WP installation.