Projection: Equirectangular projection, N/S stretching 132,898 %.
Shapefile: ISTAT Confini amministrativi Comuni 2011. Simplified with Mapshaper using "Visvalingam / effective area" algorythm at 4%.
Data:
Vector version of File:Linguistic_map_of_Italy.png.

Original data: (only for linguistic islands)  F. Bruni, "Storia della Lingua Italiana"
File:Linguistic_map_of_Italy.png
Mikima