A Formal Languages developer designs, develops, and implements formal language systems, which are mathematical structures used in computer science to describe and model computation and communication. They create formal definitions for programming languages, ensuring they follow a strict syntax and semantics. This involves creating rules for data structure, operations, and functions, and resolving language ambiguity. Their work contributes to compiler design, program interpretation, and software validation. They may also work on automating the process of language translation or code generation, and conduct research to improve the efficiency, reliability, and security of formal languages.