Foreigners drink by river joints, they say (9)
I believe the answer is:
nipponese
'foreigners' is the definition.
'drink by river joints they say' is the wordplay.
'drink' becomes 'nip' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'river' becomes 'Po' (Italian river).
'joints' becomes 'knees' (knee is a kind of joint).
'they say' indicates a 'sounds like' (homophone) clue.
'knees' is a homophone of 'nese'.
'nip'+'po'+'nese'='NIPPONESE'
(Other definitions for nipponese that I've seen before include "Japanese" , "Of Japan" .)