The Decades Progress on Code-Switching Research in NLP: A Systematic Survey on Trends and Challenges

Code-Switching, a common phenomenon in written text and conversation, has been studied over decades by the natural language processing (NLP) research community. Initially, code-switching is intensively explored by leveraging linguistic theories and, currently, more machine-learning oriented approaches to develop models. We introduce a comprehensive systematic survey on code-switching research in natural language processing to understand the progress of the past decades and conceptualize the challenges and tasks on the codeswitching topic. Finally, we summarize the trends and findings and conclude with a discussion for future direction and open questions for further investigation.