I think original phrase "Файл, ассоциированный с расширением %s,отсутствует\n" is better (but there is a typo in it - missing space after second ","). And word "ассоциированный" do sounds like Russian (and has frequent use in books and speech), and I like it more than less familiar (to me) word "сопоставление". So I think word "сопоставление" maybe only good choice if Wine already using it instead of word "ассоциированный" (I'm not sure about this because I'm using English interface with Wine). (Just a note: Russian is my native language). Anyway, in my opinion such discussion "what synonym is better" is pointless because it is just a matter of personal taste.
I do not mean "ассоциированный" и "сопоставление" synonyms.
Prase "Файл, ассоциированный с расширением %s, отсутствует" is invalid. File never is associated with extension. Program is associated. And not "File" is absent, but "File association" - "Сопоставление файлов" ("сопоставление расширений файлов соответствующим программам").
I do not have anything against synonym "ассоциированный". -- Kirill