Screen translation's just what's needed in Nice (8)
I believe the answer is:
subtitle
'screen translation's' is the definition.
(translation given on screen)
'just what's needed in nice' is the wordplay.
'just what's needed' becomes 'it' (as in 'that's it!').
'in' is an insertion indicator.
'nice' becomes 'subtle' (I've seen this before).
'it' inserted into 'subtle' is 'SUBTITLE'.
(Other definitions for subtitle that I've seen before include "minor heading" , "Translation of foreign dialogue, in a film say" , "Screen caption" , "Word found at bottom of movie or TV screen" , "small print?" .)