“Polish is a foreign language,” you say (6)
I believe the answer is:
finish
'polish' is the definition.
(thesaurus)
'foreign language you say' is the wordplay.
'foreign language' becomes 'finnish' (I've seen this before).
'you say' shows a homophone (sound like).
'finnish' is a homophone of 'FINISH'.
'is a' acts as a link.
(Other definitions for finish that I've seen before include "End, conclusion" , "Complete or terminate" , "Cease, conclude" , "Bring to an end" , "Conclude, end" .)