Rag's final edition had mixed up language (9)
I believe the answer is:
franglais
'language' is the definition.
(I know that Franglais is a type of macaronic language)
'rag's final edition had mixed up' is the wordplay.
'rag's final' anagrams to 'FRANGLAIS'.
However, I'm not clear how this is indicated.
Can you help me to learn more?
(Other definitions for franglais that I've seen before include ""Je suis happy", say" , "Blended language" , "informal version of language" , "United Nations' communication" , "Corrupt language" .)