True subject and falsehood associated with good English (5)
I believe the answer is:
liege
'true subject' is the definition.
'falsehood associated with good english' is the wordplay.
'falsehood' becomes 'lie' (lie is a kind of falsehood).
'associated with' means one lot of letters go next to another.
'good' becomes 'g' (abbreviation).
'english' becomes 'e' (abbreviation).
'lie'+'g'+'e'='LIEGE'
'and' is the link.
(Other definitions for liege that I've seen before include "Belgian city - master - servant" , "Owing feudal allegiance" , "European city" , "City in eastern Belgium" , "Chieftain" .)