Depends what it’s going to do, as a general bot, GoLang, NodeJS (aka JavaScript) or Python are good shouts.
But the “chat bot” space is fairly crowed, there are MANY existing libraries that help you do what you need. Do we need “yet” another framework. Anything GameWisp’y or other API’s is tending into the realm of “not just chat bot” than then you are talking about infrastructure…