I don’t think there is much choice to visualize it in letters other than Ahhh! And you’re right, it could be mistaken as a comfy ahh… If you do have context however, it will surely be understood.
Regarding other word choices, a rather poor alternative would be setting it with a leading w (Waahhh!) or r (Raahhh!), because those usually do not express sounds of comfort.
If by “translation” you refer to the actual transfer of the idea of “Auuuurrgghhh!”, and if your translation doesn’t have to be literally, you could use colorful language to get the horror across:
Ein furchteinflößender Schmerzensschrei ließ den Umstehenden das Blut in den Adern gefrieren.