Neural machine translation (NMT) has recently gained widespread attention because of its high translation accuracy. However, it shows poor performance in the translation of long sentences, which is a major issue in low-resource languages. It is assumed that this issue is caused by insufficient number of long sentences in the training data. Therefore, this study proposes a simple data augmentation method to handle long sentences. In this method, we use only the given parallel corpora as the training data and generate long sentences by concatenating two sentences. Based on the experimental results, we confirm improvements in long sentence translation by the proposed data augmentation method, despite its simplicity. Moreover, the translation quality is further improved by the proposed method, when combined with backtranslation.

Multimodal machine translation is an attractive application of neural machine translation (NMT). It helps computers to deeply understand visual objects and their relations with natural languages. However, multimodal NMT systems suffer from a shortage of available training data, resulting in poor performance for translating rare words. In NMT, pretrained word embeddings have been shown to improve NMT of low-resource domains, and a search-based approach is proposed to address the rare word problem. In this study, we effectively combine these two approaches in the context of multimodal NMT and explore how we can take full advantage of pretrained word embeddings to better translate rare words. We report overall performance improvements of 1.24 METEOR and 2.49 BLEU and achieve an improvement of 7.67 F-score for rare word translation.

Multimodal machine translation (MMT) is an attractive application of neural machine translation (NMT) that is commonly incorporated with image information. However, the MMT models proposed thus far have only comparable or slightly better performance than their text-only counterparts. One potential cause of this infeasibility is a lack of large-scale data. Most previous studies mitigate this limitation by employing large-scale textual parallel corpora, which are more accessible than multimodal parallel corpora, in various ways. However, these corpora are still available on only a limited scale in low-resource language pairs or domains. In this study, we leveraged monolingual (or multimodal monolingual) corpora, which are available at scale in most languages and domains, to improve MMT models. Our approach follows that of previous unimodal works that use monolingual corpora to train the word embedding or language model and incorporate them into NMT systems. While these methods demonstrated the advantage of using pre-trained representations, there is still room for MMT models to improve. To this end, our system employs debiasing procedures for the word embedding and multimodal extension of the language model (visual-language model, VLM) to make better use of the pre-trained knowledge in the MMT task. The results of evaluations conducted on the de facto MMT dataset for the English-German translation indicate that the improvement obtained using well-tailored word embedding and VLM is approximately +1.84 BLEU and +1.63 BLEU, respectively. The evaluation on multiple language pairs reveals their adoptability across the languages. Beyond the success of our system, we also conducted an extensive analysis on VLM manipulation and showed promising areas for developing better MMT models by exploiting VLM; some benefits brought by either modality are missing, and MMT with VLM generates less fluent translations. Our code is available at https://github.com/toshohirasawa/mmt-with-monolingual-data.INDEX TERMS Multimodal machine translation, natural language processing, neural machine translation, I. INTRODUCTION

The primary limitation of North Korean to English translation is the lack of a parallel corpus; therefore, high translation accuracy cannot be achieved. To address this problem, we propose a zero-shot approach using South Korean data, which are remarkably similar to North Korean data. We train a neural machine translation model after tokenizing a South Korean text at the character level and decomposing characters into phonemes. We demonstrate that our method can effectively learn North Korean to English translation and improve the BLEU scores by +1.01 points in comparison with the baseline.

We introduce our TMU system that is submitted to The 4th Workshop on Neural Generation and Translation (WNGT2020) to Englishto-Japanese (En→Ja) track on Simultaneous Translation And Paraphrase for Language Education (STAPLE) shared task. In most cases machine translation systems generate a single output from the input sentence, however, in order to assist language learners in their journey with better and more diverse feedback, it is helpful to create a machine translation system that is able to produce diverse translations of each input sentence. However, creating such systems would require complex modifications in a model to ensure the diversity of outputs. In this paper, we investigated if it is possible to create such systems in a simple way and whether it can produce desired diverse outputs. In particular, we combined the outputs from forward and backward neural translation models (NMT). Our system achieved third place in En→Ja track, despite adopting only a simple approach.