Natural Language Engineering (2020), 26, pp. 595–612 doi:10.1017/S1351324920000492 SURVEY PAPER Natural language processing for similar languages, varieties, and dialects: A survey Marcos Zampieri 1,∗ Preslav Nakov 2 and Yves Scherrer 3 1Rochester Institute of Technology, USA, 2Qatar Computing Research Institute, HBKU, Qatar and 3University of Helsinki, Finland ∗ Corresponding author. E-mail:
[email protected] Abstract There has been a lot of recent interest in the natural language processing (NLP) community in the com- putational processing of language varieties and dialects, with the aim to improve the performance of applications such as machine translation, speech recognition, and dialogue systems. Here, we attempt to survey this growing field of research, with focus on computational methods for processing similar lan- guages, varieties, and dialects. In particular, we discuss the most important challenges when dealing with diatopic language variation, and we present some of the available datasets, the process of data collection, and the most common data collection strategies used to compile datasets for similar languages, varieties, and dialects. We further present a number of studies on computational methods developed and/or adapted for preprocessing, normalization, part-of-speech tagging, and parsing similar languages, language vari- eties, and dialects. Finally, we discuss relevant applications such as language and dialect identification and machine translation for closely related languages, language varieties, and dialects. Keywords: Dialects; similar languages; language varieties; language identification machine; translation parsing 1. Introduction Variation is intrinsic to human language and it is manifested in different ways. There are four generally accepted dimensions of language variation, namely diaphasic, diastratic, diachronic,and diatopic.