The Collection extension is not used only on Wikipedia but also on other project like the French Wikibooks.
On this project the term "article" is not in use because it's not an encyclopedia but books. Instead we use "page" in a book, or "chapter".
Currently the extension still generates PDF files with Wikipedia specific words and terms that cannot be changed with some modification of one of the Mediawiki: page :
(words are in french)
"Articles" (at top of table of content)
--> should be "Chapitres"
"Sources et contributeurs de l’article"
--> should be "Sources et contributeurs du livre"
"Licence des articles"
--> should be "Licence des pages du livre"