I need an accurate translation from English to Latin for:
"Hell is the last hope for justice."

I am a very bad Latin scholar-- it has been over 35 years since Mrs
Gottlieb's Latin class-- but I'll toss out "arbitrium ultimum Hades
est."

Did they call Hell Hades back then? No, I don't mean back in the 70's...

Arbitrium ultimum Hades est conveys that Hell is the final arbiter
(one use of arbitrium is a decision by a judge, though by far the most
common meaning is will, as in "free will", librium arbitrium). There
may be a problem with gender and if Hades can be anthropomorphised to
take on the description.
 
Another possibility might be "ad Hades, semper advenio iustitia" which
should be "Justice always arrives in Hades."

I look forward to a researcher answering this question as it is a
pretty good quote. Please be gentle in berating me for my mangling of
a dead language.

I, too, am tusty as all get out in my Latin, but for a basic, prosaic
translation, I might suggest:

Infernus iustitia spes ultima est.

Though there's likely a more elegant, idiomatic way to get at the translation.

Like the earlier comment, I'm uncertain how best to convey "Hell" in
Latin.  I don't know that "Hades" is exactly right, since Hades might
simply imply an afterlife, not necessarily an unpleasant one for bad
people.  I've plugged in "Infernus" which probably isn't perfect
either, but is, obviously, where the word "inferno" comes from
(though, come to think of it, "infernus" is really more of an
adjective...)  It's possible that just using "Inferno" would work...

With a little more thought and a bit of research, I'm now thinking
that "Gehenna" might be a good Latin word for "Hell."  (It appears to
be used in at least some Latin language translations of the Bible.)

So, plugging that into my basic, prosaic, unnuanced translation gets us:

Gehenna iustitia spes ultima est.

Avernus or infernus are names alternatives for Hell.