Indeed, its curves in the two figures show either a stable (It-En) or even a slightly downward trend (De-En) that confirms the known limitations of NMT to preserve sentiment traits of the source sentences (see Section 1).
to condition the generic models and obtain the Reinforce and MO-Reinforce systems, we use the polarity-labeled German/Italian tweets in our de-velopment sets, with reward as defined in Section 2.