But so ludicrously English it's stupid (6)
I believe the answer is:
obtuse
'stupid' is the definition.
(similar in meaning)
'but so ludicrously english' is the wordplay.
'ludicrously' indicates anagramming the letters (I've seen this in other clues).
'english' becomes 'E' (abbreviation).
'but'+'so'='butso'
'butso' anagrammed gives 'obtus'.
'obtus'+'e'='OBTUSE'
'it's' acts as a link.
(Other definitions for obtuse that I've seen before include "Not very perceptive or sensitive" , "Angles could be" , "'Dense, slow (6)'" , "Blunt, not sharp or pointed" , "Lacking in insight" .)