The students' dominant language might influence how they use and process a rubric and its subsequent effect on task performance. However, our knowledge about these effects is limited. This study investigates how the dominant language of students is associated with their rubric reading patterns and their task performance in a written landscape analysis in Spanish. Participants were 80 higher education students with different dominant language (Spanish-dominant speakers, SDS; Basque-Spanish speakers, BSS) from six undergraduate programmes. We employed a randomized controlled trial in which participants used a rubric to guide their performance in a written analysis of a landscape. Participants were randomly assigned to two conditions based on the rubric order: (1) lowest to highest performance level vs (2) highest to lowest performance level. We analyzed eye-tracking data to explore reading patterns (i.e., fixation times on the rubric cells and gaze transitions between the rubric and the picture of the landscape), task performance (i.e., written landscape analysis), and self-reported cognitive load. Spanish-dominant speakers exhibited more adaptive reading patterns and performed better in the written landscape analysis with the highest-lowest performance level (PL) order rubric, compared to Basque-Spanish speakers. Additionally, fixation time on highest PL and gaze transitions between highest PL and the landscape picture were positively correlated with task performance. Our research highlights the importance of considering dominant language in rubric design and implementation, showing that strategic rubric design can enhance student performance, particularly in linguistically diverse educational settings.