When you are in a big project a multi paradigm language seems to be the only way for introducing new styles. In the stuff I am working on I can't just switch to a new language. I agree that this can create a mess though.
Absolutely, but it's such a double-edged sword. All else being equal, I love ruby, and when it comes to shitty legacy codebases, you can do worse than ruby because of the power at your disposal to work around problems. On the other hand, it's not that hard in ruby to make something that is so thoroughly fucked that there's no reasonable option but to nuke it from space.
The beauty of Java, Go and Haskell (never thought I'd use those 3 in the same sentence) is that you really have to work to fuck things up that badly.
