The purpose of this paper is to analyze the cognitive features of interface language and user language, clarify user requirements, and optimize interface design. The method steps are: First of all, clarify that interface is well-known as a display form that users can perceive through their own vision, hearing, operation, etc., as well as a direct way for interaction between software and users. Furthermore, to analyze the interface design and the multi-language features inherent in the user interface, the user language that needs to be converted at the first level is the user’s personalized language. In general, it is necessary to understand what the user’s inner true thoughts want; the second level of the user language that needs to be converted is the personalized interface that the user wants. However, at this time, the user’s requirements are described by combining natural language, graphics, and even metaphor. The result is: Through the dual conversion from user language to interface language, the combination between user requirements and interface design has been clearly defined. At least, the requirements focus has been identified, like the difference between main and auxiliary functions. Grasp this point, a targeted and concise interface design is possible. Its significance lies in: It is not only conducive to the optimization of the specific software interface function design, but also helps people to further discuss the cognitive features of the interface language and the user language in theory.