The earliest work on using discourse in machine translation that we are aware of dates back to 2000: Marcu, Carlson, and Watanabe (2000) proposed rewriting discourse trees for MT.
this research direction was largely ignored by the research community as the idea was well ahead of its time: Note that it came even before the current standard phrase-based SMT model was envisaged (Koehn, Och, and Marcu 2003).