RAF signal broadcast garbled language? (9)
I believe the answer is:
'garbled language?' is the definition.
(informal blend of French and English)
'raf signal broadcast' is the wordplay.
'broadcast' indicates an anagram (letters scattered or cast around).
'rafsignal' anagrammed gives 'FRANGLAIS'.
(Other definitions for franglais that I've seen before include "French with many English words" , ""Je suis happy", say" , "Corrupt language" , "A mix of tongues" , "informal version of language" .)