The plugin architectures that I've seen require plugins to be written in the same language as the IDE. For example, Eclipse plugins need to be written in Java.

The plugin architectures that I've seen require plugins to be written in the same language as the IDE. For example, Eclipse plugins need to be written in Java. Language servers run in a separate process to the editor, and they communicate over JSON-RPC. The nice thing about this is that the language server can be written in any programming language - which usually ends up being the language of the code being edited, rather than the language that the editor was written in. This makes it a lot easier for language servers to be written and maintained by the people who maintain the compilers for those languages, e.g. gopls is written by the Go developers, clangd is part of LLVM.