Just spotted the partial attempt at making the words (in English) rhyme & scan, had another go to finish it. I don't like my version of the penultimate verse (If it does signify Mary's virginity then 'penetrated' may be a bad choice of words!).
I also seem to have taken a couple of liberties with Joe's translation, which I assume is accurate rather than idiomatic.

GAUDETE (CELEBRATE)

Celebrate! Celebrate! for Christ the Saviour
Of the Virgin Mary's born; Celebrate!

Now the time of Grace has come, for which we have prayéd
Now let our devotions be with songs of joy arrayéd

God his manhood now takes on, Nature stands/is amazéd
Christ The King renews the world; may His name be praiséd

The closed gate of Ezekial has been penetrated
By the light out of the East, salvation's located

Thus, let our assembly praise when comes purification
Let it bless the lord, and greet the King of every nation.

Any takers to improve on this?

Joe, any major misuses of the original?

Nigel