Emperor backed an Iranian language, banning son’s imperial title (3,6)
I believe the answer is:
ras tafari
This could be a double definition.
'emperor' is the first definition.
(I've seen this before)
'imperial title' is the second definition.
(title of Ethiopian monarch Haile Selassie)
'backed an iranian language banning son's' acts as a link.
I am not very happy about this link. Some or all of it may belong to one of the definitions.
(Other definitions for ras tafari that I've seen before include "Movement whose followers worship an Ethiopian emperor" , "Royal once" , "opposed to Babylon?" .)