Ultimately elegant Irish language crisply brief (5)
I believe the answer is:
terse
'crisply brief' is the definition.
(I've seen this before)
'ultimately elegant irish language' is the wordplay.
'ultimately' says to take the final letters.
'irish language' becomes 'Erse' (Erse can mean the Irish language).
The final letter of 'elegant' is 't'.
't'+'erse'='TERSE'
(Other definitions for terse that I've seen before include "Reset to be pithy" , "Brusque and curt" , "Concise about trees" , "precise" , "Brief; abrupt" .)