Formal:
* ഞാൻ ബുദ്ധിമാനാണ് (njan buddhimaan aanu) - This is the most literal translation and is considered formal.
* ഞാൻ നല്ല ബുദ്ധിശക്തിയുള്ള ആളാണ് (njan nalla buddhishakthiyulla aalaanu) - This translates to "I am a person with good intelligence."
Informal:
* ഞാൻ കുശലനാണ് (njan kushalan aanu) - This means "I am clever" or "I am quick-witted" and is more casual.
* എനിക്ക് നല്ല മനസ്സുണ്ട് (enikku nalla manassund) - This means "I am intelligent" but also implies a good understanding of things.
* ഞാൻ ബുദ്ധിമാനാണെന്ന് പറയാം (njan buddhimaan aanennu parayam) - This is a more self-deprecating way of saying "I am smart" and translates to "I can say I am smart."
The best choice depends on the context of the conversation and your relationship with the person you are talking to.