Nothing new in extremes of Sartre’s language (7)
I believe the answer is:
slovene
'language' is the definition.
(I've seen this before)
'nothing new in extremes of sartre's' is the wordplay.
'nothing' becomes 'love' (I've seen this before).
'new' becomes 'n'.
'in' means one lot of letters goes inside another.
'extremes of' says to hollow out the word (remove centre letters).
'sartre' with its centre removed is 'se'.
'love'+'n'='loven'
'loven' placed inside 'se' is 'SLOVENE'.
(Other definitions for slovene that I've seen before include "Central European" , "One from Ljubljana" , "Language" , "Native of Ljubljana" , "Southern European" .)