when I first saw this thread I thought that Brookfield may have been able to answer, (I assumed that he may have learned some Latin in school).
-which is why I didn't answer...
My brother learned som Latin, though it has to be said that it's basically a dead/useless language!
but, nether the less.
seems there are many possibly permeatations of what you are trying to say..
ymo (immo): on the contrary, by no means/ by all means
haud : no, not at all, by no means.
despero : to be without hope, despair / despair of, give up.
despero : to have no hope, despair, give up.
spera : (n.pl.) hopes
spero : to hope for, hope.
spes : hope.
paciscor : to make a bargain or agreement, covenant, deal.
re : in
perfidia : treachery, faithlessness.
perfidiosus : treacherous, faithless
opto : to desire, wish for, want.
nec : conj, and not
non : not.
numquam : at no time, never.
nullus : not any, no, none.
fides : trust, confidence, reliance, belief, faith
so there are many possible ways of saying never trust a hope, but no way of saying that exactly.
never trust hopes - numquam fides spera
By no means trust hope - ymo fides spes
trust no hopes - fides nullus spera
trust not hope - fides nullus spes
trust and not hope - fides nec spero
trust not in hopes - fides nullus re spero
the gramatical structure should be very close to a language that is very closely tied to latin, the words appearing as they would make sense in english is probably fine, but you should perhaps look towards a more latin language for gramatical rules, (something like Italian/spanish).
pronounciation will be much like it's written as well. it's almost impossible to describe pronounciation in words, so I won't even try. but the same suggestion applies as above, for the way to say the words seek inspiration from heavily latin based languages.