That English translation looks unnatural to me
'What's happening?' and 'What's up?' both mean the same thing. 'What's doing?' is the literal translation though, and it's definitely the way I would say it, but I think it depends on where you're from.
It sounds natural to me.
First answer that has prompted me to come and comment :) certainly is unnatural in the English translation.
Really? You've never listened to Marvin Gaye?
I would be more likely to say, 'How are you doing' or 'How's it going?' Would they be correct translations?
I don’t think you’d be likely to hear what is occurring in colloquial speech.