Are you serious? In which language do you program that you don't have to use multiple libraries daily? You just talked about NPM.
In your example, the C# could output DLLs that have functions that can be called by the Java code. This can give the same encapsulation you get with your multiple services example, including separate deployments, different repo, different language, etc.
You could also use different processes. Please tell me you know what an executable is...
> Meanwhile I could set up the separate repos/microservices by the end of the day
That's because someone set it up for you, not because it's faster.
In your hypothetical scenario of "I needed to let a remote team add some functionality to my, say, Spring backend but they really prefer to write C# and have their own CI/CD system" you didn't mention that "…but we already have a fast way of setting up micro services".
> It is unfortunate that the "micro" in "microservice" is often misunderstood*
It's not, you're using the term loosely. "Two services" do not make a micro service architecture.
Sorry to be blunt, but I'm getting the feeling you're not talking out of experience, but rather repeating popular talking points.
