When it comes to working with complex data structures, one of the most popular languages is Python. Python is known for its simplicity and readability, making it a great choice for developers of all skill levels. The language also has a wide variety of libraries and frameworks, such as NumPy and Pandas, that make it easy to work with large datasets and perform complex calculations.

Another popular choice for working with complex data structures is Java. Java is an object-oriented programming language that is widely used in industry. It's known for its strong type checking, which can help prevent errors when working with complex data structures. Java also has a large and active community, which means that developers can easily find support and resources for their projects.

C++ is another programming language that is commonly used for working with complex data structures. It is known for its speed and efficiency, making it a great choice for large-scale projects. C++ also offers low-level access to memory and hardware, which can be useful when working with complex data structures.

Lastly, C# is another language that is commonly used for working with complex data structures. C# is an object-oriented language that is similar to Java in many ways. However, it is primarily designed for Microsoft's .NET Framework, which provides a wide variety of libraries and frameworks that make it easy to work with complex data structures.

In conclusion, there are many programming languages that can be used for working with complex data structures. The choice of language will depend on the specific requirements of the project and the expertise of the developer. Python, Java, C++ and C# are some of the most popular choices among developers. Each language has its own strengths and weaknesses, so it's important to consider the specific needs of the project when making a decision.