Between the 8th and 9th century the linguistic boundary between the Gallo-Romance-speaking western regions and the central and western Alemannic-speaking regions had already formed clearly, and between the 13th and the 14th century the Swiss Plateau became completely Alemannic-speaking.
Between the 8th and 9th century a clear linguistic distinction developed between Gallo-Romance-speaking western areas and Alemannic-speaking central and western regions, and by the 13th to 14th century the entire Swiss Plateau became Alemannic-speaking.