Background: In dementia-specific care, the design of the environment is regarded as an influential element in the support and maintenance of skills and can improve the quality of life of residents. To date, there is no valid instrument in the German-speaking countries with which the quality of the physical environment in residential long-term care facilities can be systematically assessed. Objective: To report the translation, linguistic validation, cultural adaptation, and content validity evaluation of the Australian Environmental Audit Tool—High Care in preparation for use in German nursing homes. Method: The procedure was guided by an adapted multistep process of the World Health Organization (1998) and included focus groups involving potential users of the new tool such as scientific experts and healthcare professionals (n = 40). Content validity indices were calculated following a two-step expert survey. Results: The final draft versions of the German Environmental Audit Tool (G-EAT) included 74 and 77 items, for non-secured units and secure units, respectively, divided into 10 key design principles according to the Australian original. The evaluation of content validity showed that cultural differences existed in several items. Conclusions: The G-EAT provides the means for conducting a valid assessment of the environmental quality of people with dementia in German nursing homes. However, its usability in healthcare research must be preceded by testing its interrater reliability.