AI is a wide field that goes beyond machine learning, deep learning, neural networks, etc. In some of these fields, the programming language does not matter at all (except for speed issues), so LISP would certainly not be a topic there.

In search or AI planning, for instance, standard languages like C++ and Java are often the first choice, because they are fast (in particular C++) and because many software projects like planning systems are open source, so using a standard language is important (or at least wise in case one appreciates feedback or extensions). I am only aware of one single planner that is written in LISP. Just to give some impression about the role of the choice of the programming language in this field of AI, I'll give a list of some of the best-known and therefore most-important planners:

**Fast-Downward:**  
*description:* the probably best-known classical planning system  
*URL:* http://www.fast-downward.org/  
*language:* C++, parts (preprocessing) are in Python  

**FF:**  
*description:* together with Fast-Downward *the* classical planning system everyone knows  
*URL:* https://fai.cs.uni-saarland.de/hoffmann/ff.html  
*language:* C

**VHPOP:**  
*description:* one of the best-known partial-order causal link (POCL) planning systems  
*URL:* http://www.tempastic.org/vhpop/  
*language:* C++  

**SHOP and SHOP2:**  
*description:* the best-known HTN (hierarchical) planning system  
*URL:* https://www.cs.umd.edu/projects/shop/  
*language:* there are two versions of SHOP and SHOP2. The original versions have been written in LISP. Newer versions (called JSHOP and JSHOP2) have been written in Java. Pyshop is a further SHOP variant written in Python.  

**PANDA:**  
*description:* another well-known HTN (and hybrid) planning system  
*URL:* http://www.uni-ulm.de/en/in/ki/research/software/panda/panda-planning-system/  
*language:* there are different versions of the planner: PANDA1 and PANDA2 are written in Java, PANDA3 is written in Scala

These were just some of the best-known planning systems that came to my mind. More recent ones can be retrieved from the International Planning Competition (IPC, http://www.icaps-conference.org/index.php/Main/Competitions), which takes place every two years. The competing planners' code is published open source (for a few years).