Subject, English, to be set by those people (5)
I believe the answer is:
theme
'subject' is the definition.
('theme' can be a synonym of 'subject')
'english to be set by those people' is the wordplay.
'english' becomes 'e' (abbreviation).
'to be set by' is a charade indicator (letters next to each other).
'those people' becomes 'them' (I've seen this before).
'e' put after 'them' is 'THEME'.
(Other definitions for theme that I've seen before include "idea of the work" , "Melody on which variations are constructed" , "Subject (of talk, text, etc)" , "Motif - 4 across" , "Topic, leitmotif" .)