Refer to Nick Nicholas’ answer to After “Quora auf Deutsch” what is the next language Quora will target? for the summary of the Lohr /Nicholas/Stefani deliberations on Quora internationalisation.
Quora will launch a non-Latin script version of the site when it fits their commercial imperatives. D’Angelo is already on record that he will give Chinese a miss, because of the impenetrability of the Chinese market (Quora raises $85 million to expand internationally and develop its ads business). Similar constraints may well apply to Russian, and to Japanese. Islamophobia among VCs may get in the way of Arabic. As already noted in Heidi Cool’s answer, the high level of English literacy in India precludes Hindi.
It’s a tossup between Russian, Japanese, and Arabic, and I suspect Portuguese will get implemented before any of them.