The final witty remark is on a Belgian/French river - for balance! (9)

'balance' is the definition.
(I know that balance can be written as equipoise)

'the final witty remark is on a belgianfrench' is the wordplay.
'final' indicates one should take the final letters.
'witty remark' becomes 'quip' (a quip is a witty remark).
'on' means one lot of letters goes inside another.
'a belgianfrench' becomes 'oe' (I can't explain this - if you can you should believe this answer much more).
The final letter of 'the' is 'e'.
'is' put inside 'oe' is 'oise'.
'e'+'quip'+'oise'='EQUIPOISE'

'river for' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?