Stifling communication in the end, doctor operates — words rarely spoken (9)
I believe the answer is:
esperanto
'words rarely spoken' is the definition.
(constructed language with very few speakers)
'stifling communication in the end doctor operates' is the wordplay.
'stifling' is an insertion indicator.
'in the end' says to take the final letters.
'doctor' indicates an anagram.
The last letter of 'communication' is 'n'.
'operates' with letters rearranged gives 'esperato'.
'n' placed within 'esperato' is 'ESPERANTO'.
(Other definitions for esperanto that I've seen before include "artificial tongue" , "Linguistic invention" , "A language; neat prose (anag.)" , "Modern language" , "Personate (anag.)" .)