Language is Queen's English (4)
I believe the answer is:
erse
'language' is the definition.
(historical term for Scottish Gaelic)
'queen's english' is the wordplay.
'queen's' becomes 'ers' (ER's).
'english' becomes 'E' (abbreviation).
'ers'+'e'='ERSE'
'is' acts as a link.
(Other definitions for erse that I've seen before include "Possibly the language" , "Kind of Gaelic for seer" , "Name sometimes given to languages of the Celts in Ireland and Scotland" , "Celtic tongue" , "Irish Gaelic language" .)