Latin Translation

Does anyone know how to translate "Break a Leg" into latin?

Crurem adflictas.

A note:
Adflicto is Latin for "I break".
Adflictas is Latin for "You break".
Both are present tense.
But your phrase is a future tense command and I am not 100% sure that adflictas is correct.
I suggest you surf on over to www.latin.fsbusiness.co.uk/ to confirm my translation.

crus, cruris is neuter and hence the accusative singular is just 'crus' not 'crurem'.
frango, ere is a better verb for 'break'.
You are quite right - the phrase is a command of sorts, but the future is not used for this in Latin - you need either the imperative voice or a present subjunctive.

so either - 'crus frangeas' (present subjunctive I think - havent got a Primer with me)
or 'crus frange' (could be wrong there about imperative singular, plural would be 'frangite' perhaps)

"Crus" is neuter, 3rd declension and you are correct--the accusative singular of "crus" is "crus"--very good.

I do not agree with you on your choice of "frango".
"Frango" suggests more of a shattering or a splintering or breaking into little pieces as in ice or pottery.

"Adflicto" has more of a "damage" or "break" nuance to it. "Adflicto" could also mean "to injure" or "to weaken" which I think goes with the expression more than "frango".

There is a verb "effringo" which has a "break open" sense to it as in making an omelette.

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Bellaque matribus detestata.
The war, hated by mothers.
(Horace, Carmina)

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A leg CAN shatter rather than merely fracture. It happened to a friend of mine who had a bad fall.