Fix strings and add German translation

[jochenklar]

This PR adds the German translation for 2.2.0 and adds minor changes to some strings in the code.

[MyPyDavid]

I had some string hard code in the front end test

        for text in OPTIONSETS_COUNTS_HEADER_INFOS:
            expect(page.locator("#main")).to_contain_text(text)
      expect(page.get_by_text(f"{IMPORT_FILTER_LABEL_TEXT} ({OPTIONSETS_COUNTS['changed']})")).to_be_visible()
E       AssertionError: Locator expected to be visible
E       Actual value: <element(s) not found> 
E       Call log:
E       LocatorAssertions.to_be_visible with timeout 5000ms
E         - waiting for get_by_text("Show only new and changes (5)")

should I add a fix for the test in here?

[MyPyDavid]

locally it does~n't~ fail, so ~trying to re-run again..~ I need to fix it (forgot to check out branch probably)

[jochenklar]

Good to go?