Research suggests that students from linguistically diverse settings may show better learning outcomes, especially at languages. However, existing studies on the topic are predominantly theoretical ones and focus on developed countries. This study empirically examines linguistic diversity and learning outcomes with respect to developing countries. Specially, it investigates the association between linguistic diversity and students' reading achievements and explores how consistent findings are across countries. It draws from PISA for Development 2018 data to compute two measures of linguistic diversity and uses hierarchical linear modeling for a quantitative empirical analysis. Results suggest that linguistic diversity as measured by the two approaches used in this study is not associated with students' reading achievements, and the lack of statistical association is consistent across countries. These findings seem to provide evidence showing that linguistic diversity does not influence learning outcomes.