Composer's name is translated — French are engaged in that (8)
I believe the answer is:
messiaen
'composer's' is the definition.
(Olivier Messiaen)
'name is translated french are engaged in that' is the wordplay.
'is translated' is an anagram indicator.
'french are' becomes 'es' ('are' in French).
'engaged' becomes 'si' (I can't explain this - if you can you should believe this answer much more).
'in that' is an insertion indicator.
'es'+'si'='essi'
'name' is an anagram of 'maen'.
'maen' enclosing 'essi' is 'MESSIAEN'.
Can you help me to learn more?
(Another definition for messiaen that I've seen is " French composer with centenary in two thousand and eight".)