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Crawl and crowd to bring machine translation to under-resourced languages

Abstract

We present a widely applicable methodology to bring machine translation (MT) to under-resourced languages in a cost-effective and rapid manner. Our proposal relies on web crawling to automatically acquire parallel data to train statistical MT systems if any such data can be found for the language pair and domain of interest. If that is not the case, we resort to (1) crowdsourcing to translate small amounts of text (hundreds of sentences), which are then used to tune statistical MT models, and (2) web crawling of vast amounts of monolingual data (millions of sentences), which are then used to build language models for MT. We apply these to two respective use-cases for Croatian, an under-resourced language that has gained relevance since it recently attained official status in the European Union. The first use-case regards tourism, given the importance of this sector to Croatia’s economy, while the second has to do with tweets, due to the growing importance of social media. For tourism, we crawl parallel data from 20 web domains using two state-of-the-art crawlers and explore how to combine the crawled data with bigger amounts of general-domain data. Our domain-adapted system is evaluated on a set of three additional tourism web domains and it outperforms the baseline in terms of automatic metrics and/or vocabulary coverage. In the social media use-case, we deal with tweets from the 2014 edition of the soccer World Cup. We build domain-adapted systems by (1) translating small amounts of tweets to be used for tuning by means of crowdsourcing and (2) crawling vast amounts of monolingual tweets. These systems outperform the baseline (Microsoft Bing) by 7.94 BLEU points (5.11 TER) for Croatian-to-English and by 2.17 points (1.94 TER) for English-to-Croatian on a test set translated by means of crowdsourcing. A complementary manual analysis sheds further light on these results.

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Fig. 1
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Notes

  1. 1.

    According to a study (Rehm and Uszkoreit 2013) that analyses the state of language technology support for 30 European languages in four areas (machine translation, speech, text analytics and language resources), Croatian is given the lowest mark out of five (weak/none) for three of the areas and the second lowest mark (fragmentary) for the remaining area (language resources).

  2. 2.

    http://www.theguardian.com/technology/2014/jul/15/twitter-world-cup-tweets-germany-brazil.

  3. 3.

    http://abumatran.eu.

  4. 4.

    http://nlp.ffzg.hr/resources/corpora/hrenwac/.

  5. 5.

    http://commoncrawl.org.

  6. 6.

    https://sites.google.com/site/amtworkshop2010/home.

  7. 7.

    http://nlp.fi.muni.cz/trac/spiderling.

  8. 8.

    http://nlp.ffzg.hr/resources/corpora/setimes/.

  9. 9.

    http://opus.lingfil.uu.se.

  10. 10.

    http://nlp.ffzg.hr/resources/corpora/ted-talks/.

  11. 11.

    http://nlp.ffzg.hr/resources/corpora/hrenwac/.

  12. 12.

    http://nlp.ilsp.gr/redmine/projects/ilsp-fc.

  13. 13.

    http://code.google.com/p/language-detection/.

  14. 14.

    http://sourceforge.net/projects/bitextor/.

  15. 15.

    http://www.httrack.com/.

  16. 16.

    http://tika.apache.org/.

  17. 17.

    http://code.google.com/p/boilerpipe/.

  18. 18.

    https://github.com/saffsd/langid.py.

  19. 19.

    \(S(D_j,D_i)\) is also obtained, since score \(S(\cdot )\) is not symmetric.

  20. 20.

    http://mokk.bme.hu/resources/hunalign/.

  21. 21.

    For our task, paragraphs are blocks of text which may contain more than one sentence.

  22. 22.

    http://www.nltk.org/.

  23. 23.

    The English–Croatian bilingual lexicon available at http://sourceforge.net/projects/bitextor/files/bitextor/bitextor-4.0/dictionaries/ was used for sentence alignment with hunalign. In addition, this tool was run with the option bisent to ensure one-to-one sentence alignments.

  24. 24.

    http://www.gala-global.org/oscarStandards/tmx/tmx14b.html.

  25. 25.

    The comparison between the sentences was performed on lowercased text from which non-alphabetic characters (spaces, punctuation, and numbers) were removed.

  26. 26.

    Fuzzy match scores measure the similarity between two strings by using the Levenshtein distance (Sikes 2007) to detect the elements (words in our case) matching between them.

  27. 27.

    http://nlp.ffzg.hr/resources/corpora/hrenwac/.

  28. 28.

    http://nlp.ffzg.hr/resources/corpora/setimes/.

  29. 29.

    http://zeljko.agic.me/resources/.

  30. 30.

    http://www.statmt.org/wmt14/translation-task.html.

  31. 31.

    https://github.com/moses-smt/mosesdecoder/tree/RELEASE-2.1.1.

  32. 32.

    http://www.statmt.org/wmt13/test.tgz.

  33. 33.

    ftp://jaguar.ncsl.nist.gov/mt/resources/mteval-v13a.pl.

  34. 34.

    http://www.umiacs.umd.edu/~snover/terp/.

  35. 35.

    http://www.ark.cs.cmu.edu/MT/paired_bootstrap_v13a.tar.gz.

  36. 36.

    While one might intuitively think that lower OOVs should correlate with better scores in terms of automatic MT evaluation metrics, this is not always the case as there are many other factors at play. MT evaluation metrics take into account word order, shifts, n-gram matching, etc. On top of these, a sizable portion of OOVs tend to be named entities, which in many cases are fine to be left untranslated, and if so whether the MT system covers them or not will not have any impact on the score produced by the MT metric.

  37. 37.

    http://cngl.ie/brazilator/#/about.

  38. 38.

    https://hub.microsofttranslator.com/.

  39. 39.

    https://github.com/nljubesi/tweetcat.

  40. 40.

    http://crowdflower.com/.

  41. 41.

    http://hdl.handle.net/11356/1049.

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Acknowledgments

This research is supported by the European Union Seventh Framework Programme FP7/2007–2013 under grant agreement PIAP-GA-2012-324414 (Abu-MaTran) and by the ADAPT Centre for Digital Content Technology, funded under the SFI Research Centres Programme (Grant 13/RC/2106) and co-funded under the European Regional Development Fund.

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Correspondence to Antonio Toral.

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Toral, A., Esplá-Gomis, M., Klubička, F. et al. Crawl and crowd to bring machine translation to under-resourced languages. Lang Resources & Evaluation 51, 1019–1051 (2017). https://doi.org/10.1007/s10579-016-9363-6

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Keywords

  • Statistical machine translation
  • Web crawling
  • Crowdsourcing