Abrupt language after concert's conclusion (5)
I believe the answer is:
terse
'abrupt' is the definition.
(I've seen this before)
'language after concert's conclusion' is the wordplay.
'language' becomes 'erse' (historical term for Scottish Gaelic).
'after' is a charade indicator (letters next to each other).
'conclusion' suggests the final letters.
The last letter of 'concert' is 't'.
'erse' after 't' is 'TERSE'.
(Other definitions for terse that I've seen before include "Short and succinct" , "Short, abrupt" , "Trees (anag.)" , "Abrupt, concise" , "Brusque, concise" .)