[rsbrux]

The description just says, "In addition, in some contexts where the book language is available, the language of the book is used.", but does not specify any "contexts".
I don't see any relevant variables other than "per_language_title_sort_articles". I neither need nor wish to set a "default_language_for_title_sort" to "tell calibre to use a language other than the user interface language". What would I put there? According to the description, the only other variable, "title_sort_articles" "is ignored (present only for legacy reasons)." Do i misunderstand you? Are there other variables I should be aware of?

P.S. Perhaps I should have mentioned that the language fields for the books mentioned in my original post are set to "Italian" and Spanish" respectively. Is calibre expecting them to be set to "ita" and "spa" instead"? The books with language set to "English" are being correctly parsed, but perhaps that is because English is my UI language.