Nowadays, the importance of communication and relationship with other countries is undeniable. Language plays a crucial role in the dissemination of science, awareness, knowledge and technology in a world where there are diverse languages, cultures and nationalities, but the need to learn a language has become essential due to the conceptual differences of languages. French has always been considered by teachers as a widespread and effective language in the world, but structural difficulties, especially in the field of grammar, have created challenges in the process of teaching French. This study seeks to decipher the reasons behind the difficulty of teaching French grammar, especially adverbs, to non-French language learners (here, English and Persian). The present research study is based on a structural comparison of the three languages (French, English and Persian). In this study, the obvious differences between these three languages, especially Persian compared to the other two languages will be analyzed in the following sections of this study. In fact, these are conceptual differences that make it difficult to study a foreign language course, and the teaching course will be enjoyable by carefully examining these differences that are rooted in the culture of each country. In other words, the depth of language differences determines the severity of the difficulty of teaching French to non-French speakers.