A language shift occurs when the people in a particular culture or sub-culture change the primary language that they use for communication. This can happen in two primary ways: by indigenous languages been replaced with regional or global languages or by the language of immigrant populations being replaced with the dominant language of the host country. When there are no more native speakers of a language, it is considered dead or extinct. As of 2011, linguists estimate that at least half of the world's 5,000 languages are considered endangered as a result of globalization.
The most common way for a language shift to happen is through formal education in a more dominant language. For example, as indigenous peoples in Central America have increasing access to education, they are more likely to become fluent in Spanish. The first language might continue to be used at home for a period of time, but gradually Spanish may replace the indigenous language for education and business. Over a few generations, the first language may fall out of use even in private settings, resulting in a language shift.
A number of factors can combine to make a language shift more or less likely. In general, the fewer people who speak a language, the greater the chances that its speakers will find it necessary to learn regional or global languages in order to get by in an interconnected society. On the other hand, if a people group is especially isolated, such as on a small cluster of islands or deep in the rainforest, they may have a better chance of maintaining their language since they have less interaction with others.
Stronger cultural ties between speakers of a language also lessen the likelihood that a complete shift will occur. Tamil speakers in Malaysia, for instance, have largely retained their own language as a result of cultural and religious differences with their Malay-speaking neighbors. Native Tamil speakers may learn either Malay or English in schools, but generally are unlikely to intermarry or culturally assimilate with the larger Malay cultural group.
There have been efforts in many areas to revive endangered languages after a shift or to prevent shifts all together. Gaelic was re-instituted in Irish schools, bringing about a small revival of the language in the middle and late 20th century. In other areas, primary education may take place in a local or indigenous language, to encourage speakers to solidify their knowledge of their mother tongue before learning the dominant language of the area.
Language shifts may also occur among immigrant populations in much the same way that they do in indigenous populations. Children of immigrants are educated in a second language, and the first language may gradually fall out of favor as immigrants become more adapted to the surrounding culture. The more immigrants there are from a particular area, however, the less likely this is to happen. In the United States, for instance, many successive generations may continue speaking Spanish since the presence of a large Spanish-speaking community makes language maintenance easier.