My preference would be not to refactor it at all. It works, you can figure out what it does, and the tests pass. Forget about it. Whoever wrote it, wrote it to

My preference would be not to refactor it at all. It works, you can figure out what it does, and the tests pass. Forget about it. Whoever wrote it, wrote it to the best of their ability to implement the requirements and style that existed at the time. The requirements changed and it now has to handle a new case? Now you can refactor it. What refactoring to choose depends on the new case you have to support - it's going to look a lot different if you need to accept a new "language" parameter than if you need to special-case another number.