We developed a methodology and a framework for automatically evaluating and filtering large-scale parallel corpora for neural machine translation (NMT). We applied six modern Quality Estimation (QE) models to score 55 million English-Ukrainian sentence pairs and conducted human evaluation on a stratified sample of 9,755 pairs. Using the obtained data, we ran a thorough statistical analysis to assess the performance of selected QE models and build linear, quadratic and beta regression models on the ensemble to estimate human quality judgments from automatic metrics. Our best ensemble model explained approximately 60% of the variance in expert ratings. We also found a non-linear relationship between automatic metrics and human quality perception, indicating that automatic metrics can be used to predict the human score. Our findings will facilitate further research in parallel corpus filtering and quality estimation and ultimately contribute to higher-quality NMT systems. We are releasing our framework, the evaluated corpus with quality scores, and the human evaluation dataset to support further research in this area.

This study addresses the challenges of learning unsupervised word representations for the morphologically rich and low-resource Ukrainian language. Traditional models that perform decently on English do not generalize well for such languages due to a lack of sufficient data and the complexity of their grammatical structures. To overcome these challenges, we utilized a high-quality, large dataset of different genres for learning Ukrainian word vector representations. We found the best hyperparameters to train fastText language models on this dataset and performed intrinsic and extrinsic evaluations of the generated word embeddings using the established methods and metrics. The results of this study indicate that the trained vectors exhibit superior performance on intrinsic tests in comparison to existing embeddings for Ukrainian. Our best model gives 62% Accuracy on the word analogy task. Extrinsic evaluations were performed on two sequence labeling tasks: NER and POS tagging (83% spaCy NER F-score, 83% spaCy POS Accuracy, 92% Flair POS Accuracy).