Here's a translation I made in 2023. I tried to keep close to the sense of every stanza, as well as have it rhyme. This makes it a bit clumsy in places, but overall I wasn't unpleased!

RIU, RIU, CHIU
(Mateo Flecha the Elder from Cancionero de Upsala)

    Riu, Riu, Chiu, Guardian of the river
    The ewe is guarded from the wolf by the Almighty Giver.
    The ewe is guarded from the wolf by the Almighty Giver.

The rabid wolf attempted the lady to bite,
But God, most powerful, defended her with might.
He wanted to make her so she could do no sin,
Even the sin of Adam could not enter therein.

The one who is born is the greatest king,
Christ The Patriarch, the flesh inhabiting.
He had redeemed by being born a man,
Although he was infinite, mortal he's become.

Many are the prophecies this coming has foretold,
And here in our days we are living to behold.
We see the God made man here on the earth
Because The Lord in heaven wished for his birth.

He comes to give the dead a new life again,
And comes to save us from the fall of man.
He is the light of day, this earthy young man,
He is the one whom John has called The Lamb.

I saw a thousand angels chanting in a throng,
Flying overhead singing a thousand songs.
Singing 'Glory be to heaven, Hosanna', every morn,
'And peace on earth to man', for Jesus he is born.

See how it is fitting the way that it was heard,
No better than a mother could God make by his word.
The one who was her father today to her was born,
And he who had raised her is now known as her son.

Now that we have all things that we desire,
Together carry presents, the infant to admire.
We will all go to him to give to him our vow,
For he has come to earth to be our equal now.