Researchers have long argued that banning the learner’s own language in the classroom “has little to do with pedagogical principles or scientific research”. Neuroscience confirm that, as this article from Cambridge University shows. More scientific references:
“The mother tongue is the greatest asset people bring to the task of foreign language learning and provides a Language Acquisition Support System.” Butzkamm, Wolfgang. (2003). We only learn language once. The role of the mother tongue in FL classrooms: Death of a dogma. Language Learning Journal.
“the potential of the mother tongue as a classroom resource is so great that its role should merit considerable attention” Atkinson, D. The mother tongue in the classroom: a neglected resource?
“neuroscience affirms that the initial acquisition of new words in a foreign language depends on the association of these items with corresponding first language items in the learner’s memory.” Sousa & Tomlinson, 2011. Differentiation and the brain: How neuroscience supports the learner-friendly classroom.
If you want to dive deeper, this review of current research indicates that there is now a substantial body of literature which supports own-language use: Hall, G., & Cook, G. (2012). Own-language use in language teaching and learning. Cambridge’s Language Teaching
“The learner’s own language has been neglected as a resource in the learning of another language and, in some contexts, it has been banned altogether. The arguments in favour of own-language exclusion are not supported by research” Kerr, P. (2015). The learner’s own language.
“Translation has long been viewed as an ineffective pedagogical tool due to its unjustifiable association to old methods of teaching, particularly the Grammar-Translation Method (GTM) and its practices.” Djelloul, D.B., & Neddar, B.A. (2017). The Usefulness of Translation in Foreign Language Teaching: Teachers’ Attitudes and Perceptions.
“An extensive and growing body of research affirms the value of using students’ home language (L1) in both second language (L2) and content learning in the classroom. In spite of this, instructional policy and practice continue to operate as though English-only approaches are axiomatic and essentially common sense.” Paterson, Kate. (2020). Disrupting the English-only status quo: Using home language as a vital resource in the classroom. 46. 5-15.
Guy Cook: Translation in Language Teaching, Oxford University Press (book) “This is a timely and important book. It is a welcome attempt to get translation out of the taboo zone in the language sciences and to show that it is well worth taking a fresh look at this age-old, but curiously neglected multilingual practice. Cook questions this neglect on many fronts, and argues convincingly for re-considering translation in language learning and teaching, claiming that the integration of translation in a teaching program is useful for most language learners.”