There are several AI engines that can do that.

Some of them are just inference engines making use of previously seen text.

But with the advent of Internet, some of them picks up keywords and googles "what is xx" etc and then brings back answers etc. They can be rather entertaining, since they can introduce very interesting twists to a dialog. And they normally have seed logic, where they look for random new subjects for the "debate".

There are software that have managed a score over 50% on the Turing test - more than 50% thought they chatted with a human...

But the only engines I have seen have been english-based, and have managed many times better language. But sending the language through one or two translation steps can quickly make almost perfect english into suitably hard to read language.

The first such program I played with was a program shipped with my Sound Blaster Pro sound card more than 20 years ago:
http://en.wikipedia.org/wiki/Dr._Sbaitso
http://www.soyacincau.com/2011/10/1...-software/