Handling OOV Words in Dialectal Arabic to English Machine Translation

Dialects and standard forms of a language typically share a set of cognates that could bear the same meaning in both varieties or only be shared homographs but serve as faux amis. Moreover, there are words that are used exclusively in the dialect or the standard variety. Both phenomena, faux amis and exclusive vocabulary, are considered out of vocabulary (OOV) phenomena. In this paper, we present this problem of OOV in the context of machine translation. We present a new approach for dialect to English Statistical Machine Translation (SMT) enhancement based on normalizing dialectal language into standard form to provide equivalents to address both aspects of the OOV problem posited by dialectal language use. We specifically focus on Arabic to English SMT. We use two publicly available dialect identification tools: AIDA and MADAMIRA, to identify and replace dialectal Arabic OOV words with their modern standard Arabic (MSA) equivalents. The results of evaluation on two blind test sets show that using AIDA to identify and replace MSA equivalents enhances translation results by 0.4% absolute BLEU (1.6% relative BLEU) and using MADAMIRA achieves 0.3% absolute BLEU (1.2% relative BLEU) enhancement over the baseline. We show our replacement scheme reaches a noticeable enhancement in SMT performance for faux amis words.