Exploring language endangerment: historical, geographical, and economic insights from multilayer language-country bipartite network analysis

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.