I'm not sure about this. For instance, Scala has a very capable Java FFI, but using it can be problematic due to the different expectations of the languages.
In Java, you represent a missing value with null, but well-typed Scala should never encounter a null. Java will also regularly raise exceptions, but Scala usually prefers wrapping values that may fail with Either. There's no clear way to automatically bridge the gap, which means falling back to Java is always going to be a necessary evil, rather than something that should be encouraged.
