Ask HN: Building a simple conversational UI – what libraries should I look at?

I'm looking to build a simple conversational/text UI for an existing application.

Need to support about 20 "commands" (ex: How many visitors did I get last week?).

Considered just creating a Domain Specific Language (many libraries for that), but want to support something closer to natural language.

What libraries should I look at? I'm primarily a Python guy, but am open to other languages.