What causes languages to go extinct?
While the English-speaking population has grown to include people all over the world, there are a large number of languages that are being spoken by fewer and fewer people and are in danger of going extinct–about a quarter of the world’s languages could have no native speakers in the near future. Recent research shows that languages approximate a lognormal distribution with respect to their number of speakers and geographical range, which means that (similar to a distribution that follows an inverse power law) there are a large number of languages that have a very small number of speakers. However, there is a distinct difference between languages with a small number of speakers and languages with a very small number of speakers (below a certain threshold, somewhere around 330 speakers)–many languages with more than this number of speakers, which is still a small number, continue to gain speakers. Below this number of speakers, languages become extinct very quickly. The researchers concluded that there is some minimum population size required for human languages to thrive. This points to an Allee effect, a positive relationship between population size and benefits to the speakers.
This is similar to the model of a market with network effects: if the more people there are who are using a good, the more others are willing to pay for it, above a certain threshold, the number of people who are using a good is likely to grow. In the case of languages, this makes sense, because the more people there are speaking a certain language, the more benefits there are to speaking that language (such as job opportunities). There are also more opportunities to learn a language with more speakers, since learning a language requires interaction with a speaker of that language. Below a certain number of speakers of a language, it becomes difficult to find opportunities to communicate using that language. Native speakers of an endangered language might think that it is more beneficial to teach their children a more widely spoken language, so that they can have more economic and political opportunities. The research found that economic growth was positively correlated with loss of language diversity, so highly developed areas like the USA have a high rate of language extinctions.
There are, of course, other factors influencing which languages are spoken by a certain number of people. It is dependent partially on political and cultural aspects, especially because the low number of speakers of some languages is due to policies enforcing the use of dominant languages. Additionally, there is no reason that people must choose one language to speak, since children can easily learn more than one language. There are some advantages to being multilingual that can outweigh the costs of learning another language.
Link to the paper: Global distribution and drivers of language extinction risk