English content still dominates in many online domains and information systems, despite native English speakers being a minority of its users. However, we know little about how language proficiency influences search behavior in these systems. In this paper, we describe preliminary results from an interactive IR experiment with book search behavior and examine how language skills affect this behavior. A total of 97 users from 21 different countries participated in this experiment, resulting in a rich data set including usage data as well as questionnaire feedback. Although participants reported feeling language constraints, a preliminary analysis of native and non-native English speakers indicate little to no meaningful differences in their search behavior.