Improve German messages

[a-leithner]

This does several things to the MessageBundle_de.properties file:

• Corrects spelling mistakes (separated compound nouns must be written with a hyphen)
• Adapts spelling to German and Austrian standards (ß - sharp s - must be used instead of "ss" in some cases except in Switzerland)
• Improves some messages which felt un-idiomatic or unnatural
• Adds missing messages (possibly some that aren't needed, but also new messages for redacting stuff)
• Brings some messages closer to their original meaning (e.g. for case-sensitivity as "schreibungsabhängig" could refer to orthographic alternatives)
• Replaces non-existent words (e.g. "Interne Farbe") or words that feel like from the wrong register (e.g. "revozieren", which is highly academical)
• Removes spacing before punctuation

I'm happy to have a discussion regarding the renaming of some of the menu items. Also, to improve readability, I would suggest switching to UTF-8 to be able to remove this jungle of escape sequences though I've tried to stick with them for now.

[a-leithner]

Unrelated to this improvement, I would also like to ask for opinions on switching to gender-neutral language in this message bundle. There are a few strings which use generic masculines (as was usual in the last decade) and which could be replaced with more inclusive writing variants (though this is not yet common in software but becomes more common in news and everyday usage).

These changes would look something like "Aktueller Benutzer" → "Aktuelle*r Benutzer*in" (String viewer.utilityPane.markupAnnotation.toolbar.filter.option.byAuthor.current.label).

[pcorless]

First off, thanks for for this. I agree 100% with a migration to Unicode, no trouble there from my point of view.

Unfortunately I lack any linguistic super powers so I'll need to to take your advice on any German grammar and conventions. However that said last updates to the DE were likely made with a Swiss dialect. I wonder if it would be a good idea to consider adding further definition for German country codes. Perhaps a base DE file and tweak for Austrian and Swiss in de_AT and de_CH files?
https://www.oracle.com/java/technologies/javase/jdk8-jre8-suported-locales.html

[a-leithner]

I'm Austrian and currently don't see the need to split message files for Germany and Austria. If we'd be dealing with month names or food items, it'd be a different story. The other key differences are idiomatic naming (of which I have found none) or different rules for combining consonants of compound nouns, though Austria's and Germany's rules are mutually "officially correct" in the respective other country (and most people won't notice).

Obviously, the changes I have made regarding ß are just outright wrong in Switzerland (they haven't used it since 1906 and removed it from their orthography a little later) so I second spinning-off a separate file for Switzerland.

Can we have a combined file for Germany and Austria and a specialized one for Switzerland, or do we have to duplicate all messages in the one for Switzerland (or even worse, create a separate, duplicated one for Austria as well)?

In any case, I can take a shot at updating this PR. (I'd be moving to Unicode in that case as well.)

[pcorless]

It's been a while since I looked the gritty details of the Java's i8n but I have this old mental model that if a string wasn't found in a subgroup it would check it's parent. Assuming my memory is correct it might be possible to only add the differences the de_CH file.

[a-leithner]

I can confirm that we can override messages from de in a de_CH file. (I was unsure whether we'd then need to have separate files for de_DE and de_AT as well, but this isn't the case it turns out.) Will push modifications shortly.