Language a scholar finally understood (5)
I believe the answer is:
argot
'language' is the definition.
(argot can mean jargon or slang)
'a scholar finally understood' is the wordplay.
'finally' suggests the final letters.
'understood' becomes 'got' (getting is a kind of understanding).
The final letter of 'scholar' is 'r'.
'a'+'r'+'got'='ARGOT'
(Other definitions for argot that I've seen before include "Particular group's jargon" , "Cant" , "Jargon - patois" , "Language of a particular group" , "Patois, vernacular" .)