Previously, Gradle supported only the Groovy language, but Kotlin adds a statically compiled language that be used for scripting and for making domain-specific languages.
"The notion behind this is really just to make build programming into a first-class engineering discipline and move it away from its historical legacy," said Miko Matsumura, chief marketing officer at Gradle. "In the past, typically, this has been done with XML configuration or even with shell scripting. It's moved up in the world of programming."