Reddit mentions of Grundkurs Philosophie Band 1. Logik

The good news is that the grammar has not changed. There are, of course, plenty of words, expressions or syntactical constructions no longer (or never been) in everyday use.

There are specialized philosophical German-English dictionaries, e.g. https://www.amazon.de/Dictionary-Philosophical-W%C3%B6rterbuch-philosophischer-Fachbegriffe/dp/3825284409

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There are index lists and encyclopedias in both languages, e.g.

English: https://en.wikipedia.org/wiki/Glossary_of_philosophy | https://plato.stanford.edu/contents.html

German: https://www.spektrum.de/lexikon/philosophie/

Maybe reading articles in those is a good preparatory exercise?

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There are also philosophy textbooks for teaching in German schools that usually only contain extracts of philosophical works with a lot of commentary, e.g. https://www.westermann.de/reihe/WEITDENK/Weiterdenken-Ethik-Philosophie

... or other literature that provides an overview and is written for a wider public, e.g. https://www.amazon.de/Grundkurs-Philosophie-Logik-Reclams-Universal-Bibliothek/dp/3150184681

Have you considered reading "Sophies Welt" by Jostein Gaarder in German? You could use it to build up some vocabulary before you go back to the authentic classics?

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For poetry, the only thing that comes to mind is a very good monolingual dictionary in combination with a poetry reading group with natives. If it it is a classic, there would also be commentaries and interpretations, e.g. as a part of the infamous "Königs Erläuterungen und Materialien" series.