For a different notation, we use (x i , y j ) where i, j ∈ {0, ..., K} to represent a pair of sentences translating from a source language i to a target language j. K + 1 languages are considered in total.
a multilingual model is usually trained by maximizing the likelihood over training sets D i,j of all available language pairs S. : where we denote L j θ (x i , y j ) = log p(y j |x i , j; θ).