Which approach involves defining acceptance tests in the stakeholders' domain language?

The approach that involves defining acceptance tests in the stakeholders' domain language is acceptance test-driven development (ATDD). This methodology emphasizes collaboration among various stakeholders, including customers, developers, and testers, to clearly define the expected behavior of the system before development begins.

By using the stakeholders' domain language, the acceptance tests become more understandable and relevant to those who will ultimately use the system, fostering better communication and ensuring that development aligns closely with user requirements. This leads to a stronger agreement on what constitutes "done" as well as clearer expectations, which can significantly improve the quality of the software delivered.

Additionally, ATDD not only helps in ensuring that the system meets requirements but also facilitates early detection of misunderstandings or ambiguities in specifications, which can be addressed collaboratively. This results in a more efficient development process and a final product that better satisfies the needs of its users.