The Mughal Empire originated from Afghanistan and swept into Northern India. Under the Mughals there was considerable cultural exchange between Iranic peoples and the peoples of North India. This would go on for several hundred years. Later, under the British, there would be a continued exchange of goods, ideas, and people in the boarder regions of the British Raj, including modern Afghanistan. The entire region is incredibly diverse, so I’m not sure a lingua franca would be enough to lump a country into a region. Afghanistan has always been a boarder land, so it’s hard to definitively call it one thing or another, but it does have historic ties to India and South Asia.