  Language endangerment is a phenomenon in which approximately 40% of languages
spoken worldwide are predicted to disappear within the next few decades,
resulting in the loss of cultures associated with these languages. To take
effective measures against language endangerment, it is essential to
quantitatively understand its characteristics because it is a phenomenon in
which historical, geographical, and economic factors are intricately
intertwined. In this study, multilayer language-country bipartite networks are
constructed using information about which countries each language is spoken in
and two types of linguistic features, namely the existence of a writing system
and the function within a country. In addition, percolation simulations are
conducted to measure how language and country networks break down according to
the extinction of languages and to identify vulnerable connections in them. In
the language network of officially used languages with their writing system,
the community analysis indicated that there were communities composed of
languages spoken over geographically separated distances. The strength of
languages revealed that the official languages in the former colonial nations,
namely English, French, Spanish, Dutch, Portuguese, and Russian, still played
significant roles in the formation of these communities. In the language and
country networks of unofficially used languages without their writing system,
the percolation simulation revealed that languages were likely to severely
disappear in the Americas, and that linguistic diversity was vulnerable in
affluent countries. The findings show that the analysis of multilayer
language-country bipartite networks has enabled a quantitative understanding of
the language endangerment occurring worldwide from historical, geographical,
and economic perspectives.
