Considering country-specific preferences in user interface (UI) design is a time-consuming task. We present a case study with German and Vietnamese users to explore how cultural theory can be applied in early design phases to support culturally sensitive design. We present an analysis of cultural dimensions and a comparison of German and Vietnamese question-and-answer (Q&A) websites. Based on the derived insights, we developed two UI concepts of a Q&A-website that differ in information architecture, navigation structure, and visual presentation. The prototypes were assessed with 14 German and 14 Vietnamese users in a think aloud setting. We were able to draw a conclusion about our initial analysis and the differing evaluation of the participants from the two countries due to their preferences regarding information retrieval, trust, and error handling. Our analysis provides first insights into the applicability of cultural theory in UI design but also opens up questions for further research.