> I just happen to write the majority of my code in Java. If tomorrow we decided to use a new language, I could pick it up in a few days...

The languages in your list are:

* declarative: HTML, CSS, Groovy (for Gradle), SQL

* scripting: Shell, Perl, JS, Groovy (for testing)

* Java-clones: C#

I found it difficult to pick up Clojure and Haskell "in a few days" when all I had was experience in those types of languages. In fact, mastering each of those languages requires a change in thinking that can only occur over a much longer time.