One of the main difficulties facing English as a Foreign Language learners in general and translation students in particular is their lack of mastery of the complexities of grammar in the target language they are learning. This study was an attempt to investigate the influence of categories of auxiliaries (auxiliaires) and present perfect (présent parfait) on Iranian sophomore translator trainees’ ability to use them in English. A total of 60 Iranian male and female sophomore EFL language learners participated in the study. They were chosen out of 90 participants through a piloted version of the Nelson-Danny Test as the homogeneity test. The selected participants were divided into two groups: an experimental group and a control group, with 30 students in each class. In the present study, the participants were subjected to a pretest, treatment, and posttest. Independent samples t-tests were used to analyze the data. The findings revealed that knowledge of French grammar, especially the présent parfait, significantly affected Iranian EFL learners' grammatical knowledge of the same notions in English. The findings could be employed by English teachers, EFL learners, and materials developers in the field of ELT in the Iranian context.
