This paper examines the effect of the default interface language on the usage of a bilingual digital library. In 2005 the default interface language of a bilingual digital library was alternated on a monthly basis between Mori and English. A comprehensive transaction log analysis over this period reveals that not only did usage in a particular language increase when the default interface language was set to that language but that the way the interface was used, in both languages, was quite different depending on the default language.