Pig pen with the French fashions (6)
I believe the answer is:
styles
'fashions' is the definition.
('style' can be a synonym of 'fashion')
'pig pen with the french' is the wordplay.
'pig pen' becomes 'sty' (where pigs are kept).
'with' means one lot of letters go next to another.
'the french' becomes 'les' ('the' in French).
'sty'+'les'='STYLES'
(Other definitions for styles that I've seen before include "Fashions and manners" , "Approaches" , "where there was a mysterious affair involving Poirot" , "Fashions or ways of doing things" , "Fashions or distinctive modes" .)