Effective Strategies in Zero-Shot Neural Machine Translation
Table 3: Effects of the proposed strategies on performance of zero-shot translation systems
['[EMPTY]', '[BOLD] System', '[BOLD] Zero-shot?', '[BOLD] German→Dutch dev2010', '[BOLD] German→Dutch tst2010', '[BOLD] German→Romanian dev2010', '[BOLD] German→Romanian tst2010']
When we applied the strategies on top of Back-Trans system, it seems that the data it used to train is sufficient to avoid the language bias problem. Thus, our strategies did not have a significant effect of performance on this system (4a vs. 4 and 4b vs. 4). But on the real zero-shot configuration (3), both strategies helped to improve the systems by notable margins. On tst2010, Target Dictionary Filtering (3a) brought an improvement of 1.07 on German→Dutch. On the same test set, Language as a Word Feature achieved the gains of 2.20 BLEU scores compared to Zero 6L (3b vs. 3). On German→Romanian zero-shot task, the improvements of our strategies were not as great as on German→Dutch, but they still helped, especially on dev2010.