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|Originally England, Scottish Lowlands and the North Sea coast from Friesland to Jutland; today worldwide|
The Anglo-Frisian languages are the Anglic (English and Scots) and Frisian varieties of West Germanic languages. The Northumbrian Language Society also considers Northumbrian a separate Anglic language.
The Anglo-Frisian languages are distinct from other West Germanic languages due to several sound changes: besides the Ingvaeonic nasal spirant law, which is present in Low German as well, Anglo-Frisian brightening and palatalization of /k/ are for the most part unique to the modern Anglo-Frisian languages:
The grouping is usually implied as a separate branch in regards to the tree model. According to this reading, English and Frisian would have had a proximal ancestral form in common that no other attested group shares. The early Anglo-Frisian varieties, like Old English and Old Frisian, and the third Ingvaeonic group at the time, the ancestor of Low German Old Saxon, were spoken by intercommunicating populations. While this has been cited as a reason for a few traits exclusively shared by Old Saxon and either Old English or Old Frisian, a genetic unity of the Anglo-Frisian languages beyond that of an Ingvaeonic subfamily can not be considered a majority opinion. In fact, the groupings of Ingvaeonic and West Germanic languages are highly debated, even though they rely on much more innovations and evidence. Some scholars consider a Proto-Anglo-Frisian language as disproven, as far as such postulates are falsifiable. Nevertheless, the close ties and strong similarities between the Anglic and the Frisian grouping are part of the scientific consensus. Therefore, the concept of Anglo-Frisian languages can be useful and is today employed without these implications.
Geography isolated the settlers of Great Britain from Continental Europe, except from contact with communities capable of open water navigation. This resulted in more Old Norse and Norman language influences during the development of Modern English, whereas the modern Frisian languages developed under contact with the southern Germanic populations, restricted to the continent.