It's okay according to the French lass (5)
I believe the answer is:
legal
'it's okay according' is the definition.
I can't tell whether this defines the answer.
'the french lass' is the wordplay.
'the french' becomes 'le' ('the' in French).
'lass' becomes 'gal' (both can mean a girl).
'le'+'gal'='LEGAL'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for legal that I've seen before include "Referring to the law" , "Relating to jurisprudence" , "Observing acts" , "Compliant with the law" , "Conforming with the law" .)