Expressing a valid requirements model is a crucial activity in a MDE context as it provides the starting point for further refinement steps that will lead to the implementation. In previous work we have proposed a requirements model from which it is possible to do simulation and high-level test generation. A requirements metamodel captures the key concepts to model the requirements and allows us to define several automatic model transformations to manipulate the requirements. In this paper, we focus on surface languages that can assist the edition of such a requirements model for simulation or testing purposes. We propose to use two different languages: a constrained natural language and UML activity diagrams. For each language, we discuss the main interesting features to express requirements and we define a model transformation to generate the corresponding requirements model.