Literary language not usually mother tongue

Thank you to the reader that pointed me to the Google Books site of the book Mother Tongues and Other Reflections on the Italian Language (2002) by Giulio C. Lepschy. The entire section on the relationship of literary language to mother tongue is on the site (thank you, Google Books!). Here is part of what Lepschy says:

"A diglossic situation, however, in which the mother tongue and the literary medium are quite distinct (either because they are different varieties of the same language or because they are different languages), seems to be prevalent in recorded history throughout the world; and the modern European situation, in which a nation-state tends to favour the use of the same idiom for literary expression and for everyday communication among the whole population, appears to be the exception rather than the norm." (page 25)

This is a research finding that I did not know about, but it clearly shows the need for the kind of multilingual literary criticism that I am pushing. What many think to be the exception (mixed-language texts, texts not in the mother tongue) turns out to be the mainstream literary tradition!