Mixing and Matching: Combining Independently Trained Translation Model Components

AbstractThis paper investigates how to combine encoders and decoders of different independently trained NMT models. Combining encoders/decoders is not directly possible since the intermediate representations of any two independent NMT models are different and cannot be combined without modification. To address this, firstly, a dimension adapter is added if the encoder and decoder have different embedding dimensionalities, and secondly, representation adapter layers are added to align the encoder’s representations for the decoder to process. As a proof of concept, this paper looks at many-to-Estonian translation and combines a massively multilingual encoder (NLLB) and a high-quality language-specific decoder. The paper successfully demonstrates that the sentence representations of two independent NMT models can be made compatible without changing the pre-trained components while keeping translation quality from deteriorating. Results show improvements in both translation quality and speed for many-to-one translation over the baseline multilingual model.