A language border is a theoretical border between languages. Such borders do not necessarily follow modern-day political borders and may cross borders or may be held entirely within the official border. The idea of the language border infers that the border is between two mutually unintelligible languages such as the border between Swedish and Finnish, rather than the border between mutually intelligible languages such as Swedish and Norwegian.
Most studies on language borders tend to try to define when one language finishes and another one starts. This is rarely an easy task because language populations are often mixed, and even in some areas with a sole dominant language, there are enclaves that speak another language. Further complications ensue when two languages mix together to form a border dialect like Limburgish. This said, nationalism has probably made language borders easier to define.
Language borders tend to cross often arbitrary political boundaries. This is most often seen in post-colonial areas such as Sub-Saharan Africa, but it can also be seen in parts of Europe. For example, Limburgish, a Germanic language similar to Dutch and German, sweeps across the southern Netherlands, eastern Belgium and a corner of northwestern Germany around Dusseldorf. Another European example is Hungarian. After the treaty of Triannon where France rewarded its allies by stripping land away from the Hungarian part of the Austro-Hungarian Empire, large numbers of ethnic Hungarians were left in Slovakia, Serbia and Romania.
Such cross-border languages raise the question of identity. Language does not automatically define a person’s identity, yet the two are often linked. This occurs when language is linked to nationality and a dominant linguistic group. This is less likely in countries without a dominant language. The language border can define politics too, as seen in Belgium, where the government is fragmented between Flemish-speaking Flanders in the north and French-speaking Wallonia in the south.
Language borders can remain fluid. Changes in borders can be caused through a number of processes. One process is the natural influence of a dominant language. In these cases, the dominant language, through linguistic osmosis, causes people to turn away from their native tongue and speak the dominant language instead. This has happened in Dalmatia with the dominance of Croatian, for example.
In other cases, the ethnic group that speaks the dominant language will seek to deny the minority language either through banning the language or by putting pressure upon it. After the Treaty of Triannon, Romania actively moved native Romanian speakers into Transylvania’s cities to dilute the number of Hungarian speakers. Meanwhile, in Slovakia, authorities tried to ban Hungarian and deny Hungarians their rights. The same has happened in Latvia with native Russian speakers after the collapse of the Soviet Union.
Linguistic borders can shift back, too. Language shift reversal (LSR) is taking place along the modern United States-Mexico border. After the US conquered the Spanish-speaking states in the southwest of the country, Spanish was slowly pushed back and replaced with English. In the late 20th century, however, the influx of native Spanish speakers has begun to push the Spanish language border back towards its original boundary.
The ideas of language borders could be applied to studies of dialects and accents. Most of these are regionally based, such as Geordie in the Northeast of England and Glaswegian in Glasgow, Scotland. A study of a dialect language border could be employed to decide when Scouse, the dialect of the Liverpool area of England, ends and when Mancunian, the dialect of Manchester, starts.