I'm doing that today with Clojure/EDN: Garden, Reagent, Clojure/ClojureScript, HoneySQL.

(You might think it cheating somewhat because HoneySQL is just a thin syntactic wrapper on SQL, but then again, if I weren't cheap/poor, I could use Datomic, where it really is the same language.)

I don't understand the analogy either but I do know that when I'm doing iOS development it's almost always all in Swift. Sometimes some C or Objective-C or even C++ smattered in but that actually kinda proves my point because when I have to deal with one of those languages in a Swift project I slow down.

Arc does, fwiw. And that’s an important design goal. There is a lot of progress left to be made in this space.

In C#, you can almost do everything in a single language (linq to sql, model binding). You still need extensible application markup language (XAML) for the view.