Fine Latin translation? Immature (9)
I believe the answer is:
infantile
'immature' is the definition.
(similar in meaning)
'fine latin translation?' is the wordplay.
'translation?' is an anagram indicator (I've seen 'translation' mean this).
'fine'+'latin'='finelatin'
'finelatin' is an anagram of 'INFANTILE'.
(Other definitions for infantile that I've seen before include "Inflate in childish way" , "Babyish" , "for kids" , "in early stage of development" .)