Text simplification (Shardlow, 2014) that rewrites a sentence into an easy-to-understand form for language learners (Petersen and Ostendorf, 2007) and children (Belder and Moens, 2010) is attracting attention.
lexical simplification (Paetzold and Specia, 2017a), which paraphrases complex words into simpler ones according to the context while maintaining the syntactic structure of the input sentence, is being actively researched (mainly in English).