I'd like to translate "Death to the enemies of mankind" into Latin. How can I do that? If there are multiple ways of saying it, I would like it structured as close to a motto as possible, since that's what I intend to use it for.
I would go with
Mors humanae gentis inimicis.
This is a literal translation that follows the original pretty closely: mors "death", humanae gentis "of the human race, of mankind", inimicis "to the enemies". Latin word order is flexible; this order sounds best to me, but others would be grammatically correct too.
(Note that if you ask Google Translate, it will tell you this means "Death is an enemy of mankind", which it does not. As has often been discussed on this site, Google Translate doesn't actually know Latin.)
A quick translation of that phrase could be something like:
"Moriendum Hostibus Hominum"
This is a straightforward translation of what you're looking for. Many words could replace moriendum in this phrase, like fatum, letum, exitium, mors etc. I chose moriendum because it rounds out the phrase with a starting -um and an ending -um. That sentential symmetry was much liked by the Romans. Also, moriendum being a verb-turned-into-a-noun (gerund) feels much more active than a plain noun like those listed above.
I have fixed my mistake; hostis is now declined properly. In response to the comments on this post, I submit that Moriendum is acceptable with an implied to be verb (est). This would give a construction like "nunc est bibendum" in Ovid's Cleopatra ode. The intended translation of my submission is "(It is the time for) dying for the enemies of mankind."