Metrics. 7 System-level BLEU scores are computed using the multi-bleu Moses support tool. Sentence-level BLEU scores are computed using NLTK (Loper and Bird, 2002). readability; 8 (3) SARI<cite> (Xu et al., 2016)</cite> , which compares the n-grams of the system output with those of the input and the human references, separately evaluating the quality of words that are added, deleted and kept by the systems.