A Language Design Developer should be hired because they can create, innovate, and optimize programming languages, making them more efficient and user-friendly. They possess a deep understanding of syntax, semantics, and compiler design. They can bridge the gap between complex coding systems and user experience, enhancing the readability and maintainability of code. This can lead to more robust software, better productivity among teams, and ultimately, a more successful project. Their unique skills can also help in debugging and problem-solving, making them an invaluable asset to any software development team.