No, but they should probably share the same runtime, have some level of interop and be garbage collected because that makes crossing the barrier between language backend and IDE frontend so much more efficient and productive.
Historically for IntelliJ that meant writing everything in Java. Nowadays plugins are written in many different languages. You could write plugins in Ruby or Python if you wanted to. They run on the JVM. You could even use C++ and get the same benefits because GraalVM can run C++ on the JVM itself, i.e. it will apply GC to the C++ parts so you don't have to worry about ownership across the interface. But that'd be an advanced move and I don't think anyone has tried that; for such big gaps in language they tend to fall back on the more conservative multi-process model again. Stuff like Sulong is too new to have made such an impact.
Atom would have different internal data structures than VS Code.
LSP doesn't solve that. It either forces everyone to implement the LSP model and data structures, or you have a mismatch and translation anyway.
Historically for IntelliJ that meant writing everything in Java. Nowadays plugins are written in many different languages. You could write plugins in Ruby or Python if you wanted to. They run on the JVM. You could even use C++ and get the same benefits because GraalVM can run C++ on the JVM itself, i.e. it will apply GC to the C++ parts so you don't have to worry about ownership across the interface. But that'd be an advanced move and I don't think anyone has tried that; for such big gaps in language they tend to fall back on the more conservative multi-process model again. Stuff like Sulong is too new to have made such an impact.
Atom would have different internal data structures than VS Code.
LSP doesn't solve that. It either forces everyone to implement the LSP model and data structures, or you have a mismatch and translation anyway.