Software Developer for Code Optimization

I'm looking for an experienced software developer to optimize and refactor an existing codebase without changing its functionality, with a strong focus on improving performance and maintainability. The ideal candidate will have a keen eye for detail and a solid understanding of software development best practices. This is a part-time role with a project scale of small, expected to last less than a month. Please start your proposal by telling me which programming languages you have the most experience optimizing.