Cross-lingual alignments of ELMo contextual embeddings
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Building machine learning prediction models for a specific NLP task requires sufficient training data, which can be difficult to obtain for low-resource languages. Cross-lingual embeddings map word embeddings from a low-resource language to a high-resource language so that a prediction model trained on data from the high-resource language can also be used in the low-resource language. To produce cross-lingual mappings of recent contextual embeddings, anchor points between the embedding spaces have to be words in the same context. We address this issue with a new method for creating datasets for cross-lingual contextual alignments. Based on that, we propose novel cross-lingual mapping methods for ELMo embeddings. Our linear mapping methods use existing vecmap and MUSE alignments on contextual ELMo embeddings. Our new nonlinear ELMoGAN mapping method is based on GANs and does not assume isomorphic embedding spaces. We evaluate the proposed mapping methods on nine languages, using two downstream tasks, NER and dependency parsing. The ELMoGAN method performs well on the NER task, with low cross-lingual loss compared to direct training on some languages. In the dependency parsing, linear alignment variants are more successful.
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