TranspLan is a domain-specific language proposed for modeling transparency requirements in business information systems. It is based on four reference models of transparency: the Transparency Stakeholders' Wheel, Transparency Depth Pyramid, Transparency Achievement Spectrum, and information quality dimensions. TranspLan includes graphical representations like the Shield Diagram and textual specifications for stakeholders' transparency requirements and information elements. It was applied in a case study of a university marking scheme to identify transparency mismatches and leakages. The language aims to provide a rigorous way to conceptualize and analyze transparency requirements.