In recent years, methods based on string kernels have demonstrated remarkable performance in various text classification tasks ranging from authorship identification (Popescu and Grozea, 2012) and sentiment analysis (Giménez-Pérez et al., 2017; to native language identification (Popescu and Ionescu, 2013; Ionescu et al., 2014 Ionescu et al., , 2016 , dialect identification (Ionescu and Popescu, 2016b;<cite> Ionescu and Butnaru, 2017</cite>; and automatic essay scoring (Cozma et al., 2018) .