Hans Kuhn (philologist) in the context of "University of Kiel"

The Anglo-Frisian languages are a proposed sub-branch of the West Germanic languages encompassing the Anglic languages (English, Scots, extinct Fingallian, and extinct Yola) as well as the Frisian languages (North Frisian, East Frisian, and West Frisian). While this relationship had considerable support historically, many modern scholars have criticized it as a valid phylogenetic grouping. Instead, they believe that the Ingvaeonic languages comprised a dialect continuum which stretched along the North Sea, finally diverging into distinct languages – Old English, Pre–Old Frisian, and Old Saxon – during the Migration Period in the 5th century. There are still proponents of an Anglo-Frisian node in the West Germanic tree, citing strong archeological and genetic evidence for the comingling of these groups. In the 1950s, Hans Kuhn argued that the two languages diverged at the Ingvaeonic level, but later "converged". He argued that this convergence explained the striking similarity of the two languages while also explaining the issues in chronology. This view has been dismissed as improbable given the geographic divide.

The Anglo-Frisian languages have been distinguished 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 Nordwestblock (German, "Northwest Block") is a hypothetical Northwestern European cultural region that some scholars propose as a prehistoric culture in the present-day Netherlands, Belgium, far-northern France, and northwestern Germany, in an area approximately bounded by the Somme, Oise, Meuse and Elbe rivers, possibly extending to the eastern part of what is now England, during the Bronze and Iron Ages from the 3rd to the 1st millennia BCE, up to the onset of historical sources, in the 1st century BCE.

The theory was first proposed by two authors working independently: Hans Kuhn and Maurits Gysseling, whose proposal included research indicating that another language may have existed somewhere in between Germanic and Celtic in the Belgian region.