add German translation

[Ljon4ik4]

This PR adds German language support.

Current breakages related to lean4game

The German translation uses the newer format with §-placeholders. This causes two problems rooted rather in lean4game than NNG4:

• lean4game seems to change the key in the translation file if there is an escaped quote (\\" instead of \"), (it does not match lean-i18n), there is an issue Invalid escaping of translation strings lean4game#411

• The other problem concern the infoview on the right, for some entries (rw rfl) the translations are not loaded. It can be fixed by changing in client/src/components/infoview/main.tsx, ExerciseStatement , ca. line 149
  (This is the line in the pinned version of lean4game, it probably would look different with the current one):

-          ... + t(data?.descrText, {ns: gameId})}
+          ... + gT(data?.descrText)}

I don't really know how to resolve this, it seems that there are two things to wait for:

• The issues get fixed in lean4game
• the corresponding lean4game version starts being used for NNG4

Notes:

• The list of Theorems is sometimes called list of Lemmas, I added an explanation that Lemmas are 'small theorems' at one point in the German version (Also I indicated at one spot that 'Theorem' and 'Satz' are synonymous in German)
• In Multiplication.L08addmul there seems to be a small error that 'addition distributes over multiplication' rather than vice-versa (the German matches the English, i.e. I did not fix it yet)
• A few placeholders were translated manually (removing the placeholder), to fit German sentence structure.

AI use disclosure

An initial translated was created using claude OPUS, then I manually ran through all the entries and changed things which seemed strange and played through the full game to catch further errors.

[TentativeConvert]

Vielen Dank! Ich habe großes Interesse an einer deutschen Übersetzung des NNG, bin aber gerade im Urlaub und kann mir das nicht genauer ansehen. Wahrscheinlich komme ich erst im September dazu.

[TentativeConvert]

Die technischen Probleme sollten in der neuesten Version von lean-i18n behoben sein, aber der Update-Vorgang ist alles andere als einfach.

[TentativeConvert]

Für den deutschen Titel wäre übrigens "Glasperlenspiel" mein erster, "Zahlenspiele" mein zweiter Favorit.

[Ljon4ik4]

Dankeschön, die Titel klingen sehr gut.
Ich glaube Zahlenspiele wäre dann mein Favorit.

Schönen Urlaub und bis September!

[TentativeConvert]

@Ljon4ik4 Ich habe heute an der Übersetzung gearbeitet, aber ich habe hier keine Schreibrechte. Könntest Du mich zu Deinem Fork als Collaborator hinzufügen?

[Ljon4ik4]

@TentativeConvert
Ja, gerne, sollte erledigt sein. Sag Bescheid, wenn du mehr Rechte im benötigst, als per Default gegeben sind.

[TentativeConvert]

I reviewed this today and made some changes. I would be very happy for this to be merged, assuming @Ljon4ik4 is also happy with my edits.

There are only a few points that might potentially be controversial:

• The game is now called "Zahlenspiele" in the translation, not "Natürliches-Zahlen-Spiel", which I find too clunky.
• The translation uses generic feminine throughout (Nutzerin, Mathematikerin, …).
• I decided to pair "Ziel" (goal) with the verb "erreichen" rather than "lösen" or "schließen". This differs from the English original but feels more natural to me.

Some further conscious decisions are documented in the file Glossar-de.csv.

[Ljon4ik4]

Thanks a lot, I am very happy with the changes and improvements (especially with the controversial ones)!

[TentativeConvert]

Commit f787b2e should be a small update after fixing the issues in the English source mentioned above. Unfortunately, it seems the line wrapping changed in the pot and po files, so the diff is very noisy and unusable.
Sorry about that.

[TentativeConvert]

A preview of the game that includes this translation is now available at https://adam.math.hhu.de/#/g/tentativeconvert/nng4/.

@Ljon4ik4 Please give me a thumbs-up if/as soon as you're happy with this, then I'll ask the maintainers to merge.

[Ljon4ik4]

Thanks a lot, I am happy with it!
Only thing I would change still is adding your name to the translation credits.

[TentativeConvert]

@Ljon4ik4 This is live now.

[Ljon4ik4]

Thanks a lot!