Modelling and Optimizing on Syntactic N-Grams for Statistical Machine Translation Rico Sennrich author 2015 text journal article Transactions of the Association for Computational Linguistics continuing MIT Press Cambridge, MA periodical academic journal sennrich-2015-modelling 10.1162/tacl_a_00131 https://aclanthology.org/Q15-1013/ 2015 3 169 182