[i_s]

I'd argue .NET isn't actually that great of a multi language platform. We have a mixed F# and C# solution at work, and that split sometimes causes a lot of friction. If you have some C# code that depends on F# code, that constrains your ability to have F# code depend on C# code. You need to be very careful about how you organize your work to get a good solution (more than on other platforms.)

In the JVM world, mixing languages works a lot better, because you can compile .class files instead of whole assemblies. So mixing clojure and Java, for example, is very easy to do in any order.