(2016) propose languageadversarial training that does not directly depend on parallel corpora, but instead only requires a set of bilingual word embeddings (BWEs).
the multilingual transfer setting, although less explored, has also been studied (McDonald et al., 2011;Naseem et al., 2012;Täckström et al., 2013;Hajmohammadi et al., 2014;Zhang and Barzilay, 2015;Guo et al., 2016), showing improved performance compared to using labeled data from one source language as in bilingual transfer.