And the winner:
United Duchies of Cornwall and Cornwall
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The United Duchies of Cornwall and Cornwall, commonly known as the Two Cornwalls, came about following the death of Mark V of Insular Cornwall (Sx: Cornweallas) without surviving issue and so the territories passed to Alan IV of Continental Cornwall (Gl: Cornouaille).
The Two Cornwalls consisted of Insular Cornwall on South West Peninsula of Great Britain and Continental Cornwall on the Lesser Britain Peninsula of Gaul, both linguistically distinct from their neighbours - Saxon-speaking Wessex in Great Britain and Gallo-speaking Normandy in Gaul - but speaking two dialects of the same Cornish language.