Yes, there's Google Translate, but all know that's only reliable for getting the general meaning across. I'd like this to be a little more precise.
Google suggests "Ordo Tenebris Mundi" or "Ordo Tenebras Mundi". However, as near as I can tell, "tenebris" and "tenebras" are both nouns and the adjectival form is "tenebrosus", yielding Ordo Tenebrosus Mundi. Sticking that into Google Translate, unfortunately, does not net me "Dark World Order" but "order a dark world", like it's an item on a menu.
On the off chance it's not instantly obvious, we're talking vampire fiction. Plenty of them are old enough to recall when Latin was a lingua franca, at least for the educated, so it's not like the name's been dreamt up by kids who found a Latin/English dictionary, who could be expected to bungle it.