This document explores language interaction in software projects. It analyzes the Apache Hadoop project to address three research questions. RQ1 finds that over 50% of commits involve more than one language. RQ2 finds that C, SH, properties, and XML files interact most with other languages. RQ3 finds that while cross-language modules generally are not more defect-prone, some language pairs like C-Java have significantly more defects in cross-language modules. The study provides initial evidence on language interactions in software but notes threats from confounding factors and the single-project scope.