The Dothraki version could be
Anha afichak reki anni ma vorsasoon ma qoyoon, ma mori fini vazzisi yera adrivoe k'athawazari.
There tends to be a little bit of uncertainity, since we don't know everything DJP has about Dothraki, ans since we are erring humans, but this is fairly solid text, I'd say.
There's also the question of how to translate. It's never completely straightforward. To give some idea on the word/syntax choices, here's a differrent/more literal translation back from Dothraki:
I will retrieve what is mine with fire, with blood, and those who will hurt you will die screamingly.
I can also make some attempt on writing this down, as I'm not completely hopeless with callighraphy n' stuff. What kind of style are you aiming at? There's no in-world writing system for Dothaki (and no realized in-world writing system for Valyrian, for that matter), so the most sensible choice is probably some mediaval-ish fraktur style or even more primitive crude majuscule. Do you want easy legibility for a modern reader or can the font have some more exotic qualities?
