A Stronger Baseline for Multilingual Word Embeddings

Levy, Søgaard and Goldberg’s (2017) S-ID (sentence ID) method applies word2vec on tuples containing a sentence ID and a word from the sentence. It has been shown to be a strong baseline for learning multilingual embeddings. Inspired by recent work on concept based embedding learning we propose SC-ID, an extension to S-ID: given a sentence aligned corpus, we use sampling to extract concepts that are then processed in the same manner as S-IDs. We perform experiments on the Parallel Bible Corpus across 1000+ languages and show that SC-ID yields up to 6% performance increase in a word translation task. In ad- dition, we provide evidence that SC-ID is easily and widely applicable by reporting competitive results across 8 tasks on a EuroParl based corpus

A Multilingual BPE Embedding Space for Universal Sentiment Lexicon Induction

We present a new method for sentiment lex- icon induction that is designed to be appli- cable to the entire range of typological di- versity of the world’s languages. We eval- uate our method on Parallel Bible Corpus+ (PBC+), a parallel corpus of 1593 languages. The key idea is to use Byte Pair Encodings (BPEs) as basic units for multilingual em- beddings. Through zero-shot transfer from English sentiment, we learn a seed lexicon for each language in the domain of PBC+. Through domain adaptation, we then gener- alize the domain-specific lexicon to a general one. We show – across typologically diverse languages in PBC+ – good quality of seed and general-domain sentiment lexicons by intrin- sic and extrinsic and by automatic and human evaluation. We make freely available our code, seed sentiment lexicons for all 1593 languages and induced general-domain sentiment lexi- cons for 200 language

Character-level and syntax-level models for low-resource and multilingual natural language processing

There are more than 7000 languages in the world, but only a small portion of them benefit from Natural Language Processing resources and models. Although languages generally present different characteristics, “cross-lingual bridges” can be exploited, such as transliteration signals and word alignment links. Such information, together with the availability of multiparallel corpora and the urge to overcome language barriers, motivates us to build models that represent more of the world’s languages. This thesis investigates cross-lingual links for improving the processing of low-resource languages with language-agnostic models at the character and syntax level. Specifically, we propose to (i) use orthographic similarities and transliteration between Named Entities and rare words in different languages to improve the construction of Bilingual Word Embeddings (BWEs) and named entity resources, and (ii) exploit multiparallel corpora for projecting labels from high- to low-resource languages, thereby gaining access to weakly supervised processing methods for the latter. In the first publication, we describe our approach for improving the translation of rare words and named entities for the Bilingual Dictionary Induction (BDI) task, using orthography and transliteration information. In our second work, we tackle BDI by enriching BWEs with orthography embeddings and a number of other features, using our classification-based system to overcome script differences among languages. The third publication describes cheap cross-lingual signals that should be considered when building mapping approaches for BWEs since they are simple to extract, effective for bootstrapping the mapping of BWEs, and overcome the failure of unsupervised methods. The fourth paper shows our approach for extracting a named entity resource for 1340 languages, including very low-resource languages from all major areas of linguistic diversity. We exploit parallel corpus statistics and transliteration models and obtain improved performance over prior work. Lastly, the fifth work models annotation projection as a graph-based label propagation problem for the part of speech tagging task. Part of speech models trained on our labeled sets outperform prior work for low-resource languages like Bambara (an African language spoken in Mali), Erzya (a Uralic language spoken in Russia’s Republic of Mordovia), Manx (the Celtic language of the Isle of Man), and Yoruba (a Niger-Congo language spoken in Nigeria and surrounding countries)

Distributed representations for multilingual language processing

Distributed representations are a central element in natural language processing. Units of text such as words, ngrams, or characters are mapped to real-valued vectors so that they can be processed by computational models. Representations trained on large amounts of text, called static word embeddings, have been found to work well across a variety of tasks such as sentiment analysis or named entity recognition. More recently, pretrained language models are used as contextualized representations that have been found to yield even better task performances. Multilingual representations that are invariant with respect to languages are useful for multiple reasons. Models using those representations would only require training data in one language and still generalize across multiple languages. This is especially useful for languages that exhibit data sparsity. Further, machine translation models can benefit from source and target representations in the same space. Last, knowledge extraction models could not only access English data, but data in any natural language and thus exploit a richer source of knowledge. Given that several thousand languages exist in the world, the need for multilingual language processing seems evident. However, it is not immediately clear, which properties multilingual embeddings should exhibit, how current multilingual representations work and how they could be improved. This thesis investigates some of these questions. In the first publication, we explore the boundaries of multilingual representation learning by creating an embedding space across more than one thousand languages. We analyze existing methods and propose concept based embedding learning methods. The second paper investigates differences between creating representations for one thousand languages with little data versus considering few languages with abundant data. In the third publication, we refine a method to obtain interpretable subspaces of embeddings. This method can be used to investigate the workings of multilingual representations. The fourth publication finds that multilingual pretrained language models exhibit a high degree of multilinguality in the sense that high quality word alignments can be easily extracted. The fifth paper investigates reasons why multilingual pretrained language models are multilingual despite lacking any kind of crosslingual supervision during training. Based on our findings we propose a training scheme that leads to improved multilinguality. Last, the sixth paper investigates the use of multilingual pretrained language models as multilingual knowledge bases

Embedding Learning Through Multilingual Concept Induction

We present a new method for estimating vector space representations of words: embedding learning by concept induction. We test this method on a highly parallel corpus and learn semantic representations of words in 1259 different languages in a single common space. An extensive experimental evaluation on crosslingual word similarity and sentiment analysis indicates that concept-based multilingual embedding learning performs better than previous approaches