Abstract
The organizers of the annual Workshop on Machine Translation (WMT) prepare and distribute parallel corpora that can be used to train systems for the shared tasks. Two core types of corpora are the News Commentary corpus and the Europarl corpus.
Both are available in several language pairs, always between English and another European language: cs-en, de-en, es-en and fr-en. The corpora are not multi-parallel.
They come from the same source and there is significant overlap but still some sentences are translated to only a subset of the languages. The bi-parallel subsets do not all have the same number of sentence pairs.
Such corpora cannot be directly used to train a system for e.g. de-cs (German-Czech). However, we can use English as a pivot language.
If we identify the intersection of the English parts of cs-en and de-en, we can take the non-English counterparts of the overlapping English sentences to create a de-cs parallel corpus. That is what this software does.