  Neural Machine Translation (NMT) has been widely used in recent years with
significant improvements for many language pairs. Although state-of-the-art NMT
systems are generating progressively better translations, idiom translation
remains one of the open challenges in this field. Idioms, a category of
multiword expressions, are an interesting language phenomenon where the overall
meaning of the expression cannot be composed from the meanings of its parts. A
first important challenge is the lack of dedicated data sets for learning and
evaluating idiom translation. In this paper we address this problem by creating
the first large-scale data set for idiom translation. Our data set is
automatically extracted from a widely used German-English translation corpus
and includes, for each language direction, a targeted evaluation set where all
sentences contain idioms and a regular training corpus where sentences
including idioms are marked. We release this data set and use it to perform
preliminary NMT experiments as the first step towards better idiom translation.
