This week I will comment on a preprint Cross-lingual hate speech detection based on multilingual domain-specific word embeddings by authors from the University of Chile.

The pre-print evaluates the possibility of cross-lingual transfer of models for hate speech detection, i.e., training a model in one language and testing it in a different language. Hate speech detection is a particularly tough task for model transfer because many of the words have a different meaning or at least different connotations when used in hate speech than in their more standard use. An example from the paper says that the Italian word “migranti” is usually translated into English as migrants, but in the hate speech context, it typically means illegal immigrants – which are in the context of American hate speech usually called “illegals” and not “migrants”.

The cross-lingual representations for zero-shot cross-lingual transfer of hate speech models should be thus very contextualized because they need to identify the very special context-dependent meaning. In this case, we want the embeddings to be not only aware of the syntactic and semantic context, but also to do some sort of pragmatic inference. In other words, cross-lingual transfer, in this case, would require to represent the pragmatics regardless of the culture-specific practices. The authors of the paper are primarily interested in detecting hate speech, but for me, their experiments are a test of the cultural neutrality of multilingual contextual representations.

The paper test several input representations as an input to a classifier:

  1. Multilingual BERT;

  2. Standard aligned static word embeddings; and

  3. Word embeddings aligned specifically for the purpose of hate speech.

The later alignment uses a resource called Hurtlex, a lexicon of offensive, aggressive, and hateful words in over 50 languages with quite a rich annotation including mutual translation of the items. What an incredible resource!

When trained and tested in the same languages, multilingual BERT is clearly the best choice. The models benefit from the rich contextualization of the representation compared to the static embeddings. This is however not true for the cross-lingual transfer. The cross-lingual transfer is dominated by the word embeddings that were aligned using the Hurtlex lexicon. This result shows that multilingual BERT failed to recognize the pragmatics in a language- or culture-neutral way. The domain contextualization of word embeddings outperforms sentence contextualization of multilingual BERT despite the clear disadvantages of static word embeddings. The task that requires even more contextualization than usual NLP tasks has better results with static embeddings.

The results (although if I were the reviewer of the paper, I would harshly some methodological issues) raise many questions. Can we make the multilingual contextual embeddings culturally neutral? Would training the representations on less scholarly-looking texts make the models more aware of the pragmatics? Is there a more direct way of measuring cultural neutrality, so we can optimize for it during training?