One way I've done it in the past is via sub processes talking via stdin/stdout. Another way I've done it is just via a regular REST API.

You'll never get enough performance for a lot of tasks if you need to pass a lot of data between applications. But depending on your needs it's more than serviceable. The benefit of this is that plugins don't need to be written in Go, as you have a simple interface.

A good example of this is something like LSP. LSP plugins are abundant and each one is written in a different language. VSCode is Typescript, the Go language server is written in Go. Both can speak to eachother fast enough.