  One central mystery of neural NLP is what neural models "know" about their
subject matter. When a neural machine translation system learns to translate
from one language to another, does it learn the syntax or semantics of the
languages? Can this knowledge be extracted from the system to fill holes in
human scientific knowledge? Existing typological databases contain relatively
full feature specifications for only a few hundred languages. Exploiting the
existence of parallel texts in more than a thousand languages, we build a
massive many-to-one neural machine translation (NMT) system from 1017 languages
into English, and use this to predict information missing from typological
databases. Experiments show that the proposed method is able to infer not only
syntactic, but also phonological and phonetic inventory features, and improves
over a baseline that has access to information about the languages' geographic
and phylogenetic neighbors.
