It's not about you in French dialect (6)
I believe the answer is:
patois
'dialect' is the definition.
(I know that patois is a type of dialect)
'it's not about you in french' is the wordplay.
'it's not' becomes 'pas' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'you in french' becomes 'toi' (I've seen this in another clue).
'pas' going around 'toi' is 'PATOIS'.
Can you help me to learn more?
(Other definitions for patois that I've seen before include "Dialect or non-standard language" , "Form of language" , "'Argot, vernacular (6)'" , "Informal local dialect" , "Spoken regional dialect" .)