Question married couple in French (4)
I believe the answer is:
when
'question' is the definition.
'married couple in french' is the wordplay.
'married couple' becomes 'WH' (abbreviations for wife and husband).
'in french' becomes 'en' ('in' in French).
'wh'+'en'='WHEN'
(Other definitions for when that I've seen before include "Say it when you''ve had enough" , "As soon as" , "At what time?" , "stop pouring the drink" , "Over what period?" .)