There are several programming languages that are commonly used for artificial intelligence (AI) projects. Here are some of the most popular ones:

1. Python: Python is one of the most popular programming languages for AI development due to its simplicity, flexibility, and large number of libraries. It has libraries like NumPy, Pandas, and TensorFlow that are commonly used for data analysis and machine learning.

2. R: R is another popular language for AI development, especially for statistical computing and data visualization. It has a large number of libraries like ggplot2, dplyr, and caret, which are commonly used for data analysis and machine learning.

3. Java: Java is a widely used programming language for enterprise applications, and it has a number of libraries like Weka and Deeplearning4j that are commonly used for AI development.

4. C++: C++ is a high-performance language that is often used for developing AI applications that require high-speed processing and memory management, such as computer vision and robotics.

5. Lisp: Lisp is an older programming language that is still used for AI development, particularly for natural language processing and expert systems.

Ultimately, the choice of programming language for an AI project depends on several factors such as the project requirements, the developer's expertise, and the availability of libraries and tools.