Quantifying the driving factors for language shift in a bilingual region

Significance Languages are an important part of our culturally diverse world, yet many of today’s languages are in danger of dying out. To save endangered languages, one must first understand the dynamics behind language shift: what are the driving factors of people giving up one language for another? Here, we model language dynamics in time and space starting from empirical data. We show that it is the interaction with speakers of the same language that fundamentally determines spread and retreat of a language. This means that a minimum-sized neighborhood of speakers interacting with each other is essential to preserve the language. Many of the world’s around 6,000 languages are in danger of disappearing as people give up use of a minority language in favor of the majority language in a process called language shift. Language shift can be monitored on a large scale through the use of mathematical models by way of differential equations, for example, reaction–diffusion equations. Here, we use a different approach: we propose a model for language dynamics based on the principles of cellular automata/agent-based modeling and combine it with very detailed empirical data. Our model makes it possible to follow language dynamics over space and time, whereas existing models based on differential equations average over space and consequently provide no information on local changes in language use. Additionally, cellular automata models can be used even in cases where models based on differential equations are not applicable, for example, in situations where one language has become dispersed and retreated to language islands. Using data from a bilingual region in Austria, we show that the most important factor in determining the spread and retreat of a language is the interaction with speakers of the same language. External factors like bilingual schools or parish language have only a minor influence.