"Mi hijo es inteligente."
Translation:My son is intelligent.
I'm assuming so. Word for word translations don't always work, and not all words in one language have a word in another language. In English intelligent is synonymous with smart although it is a stronger word, so inteligente is probobly the closest translation. I don't know for sure so don't take my word as scripture, but that's how I understand it.
I agree with T.J. Also to add that listo means smart when used with ser.
Mi hijo es listo. My son is smart.
Mi hijo está listo. My son is ready.