  Most current machine translation models are mainly trained with parallel
corpora, and their translation accuracy largely depends on the quality and
quantity of the corpora. Although there are billions of parallel sentences for
a few language pairs, effectively dealing with most language pairs is difficult
due to a lack of publicly available parallel corpora. This paper creates a
large parallel corpus for English-Japanese, a language pair for which only
limited resources are available, compared to such resource-rich languages as
English-German. It introduces a new web-based English-Japanese parallel corpus
named JParaCrawl v3.0. Our new corpus contains more than 21 million unique
parallel sentence pairs, which is more than twice as many as the previous
JParaCrawl v2.0 corpus. Through experiments, we empirically show how our new
corpus boosts the accuracy of machine translation models on various domains.
The JParaCrawl v3.0 corpus will eventually be publicly available online for
research purposes.
