How to open .jar minecraft plugin to change it?

Question

Java

There is a plug-in for paper core, but damn it is in German, I would like to open it and change the language

Answer 1

In short, learn reverse engineering.
Jar is in fact the same zip. But inside the archive are class files (bytecode). Accordingly, you need to decompile them into source codes or you can search for source codes (source code) on github, bitbucket, etc. After all, this is an open source project.
You can start with this similar question:
https://stackoverflow.com/questions/647116/how-to-...
Better yet, start learning the language itself, and then there will be relatively fewer questions.

Answer 2

Download InteliJ IDE, throw *.class files there, you will get a relatively readable java code, which then you will have to:
1. assemble into the project that it is.
2. Restore dependencies (usually they lie nearby)
3. Restore the code (rewrite places that the decompiler presented clumsily / as is, variable names, etc.)
And yes, the decompiler cannot decipher something that is not there, for example, some kind of left api 100% turns into trash that will have to be added by hand.
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