English equivalent of komorebi (木漏れ日) — "sunshine filtering through leaves"

Though not exactly the same, crepuscular rays (also known as god rays) come close to what you are asking for.

a streak of light that seems to radiate from the sun shortly before or after sunset when sunlight shines through a break in the clouds or a notch in the horizon line and illuminates atmospheric haze or dust particles

It's often used as a special effect in games.

Wikipedia includes a list of alternative names, some of which are more idiomatic than the latin derived crepuscular:

• Backstays of the sun – a nautical term, from the fact that backstays that brace the mast of a sailing ship converge in a similar way
• Cloud breaks
• Jacob's Ladder
• Ropes of Maui – (originally. taura a Maui) from the Maori tale of Maui Potiki restraining the sun with ropes to make the days longer
• Shafts of light
• Sun drawing water – from the ancient Greek belief that sunbeams drew water into the sky (an early description of evaporation)
• Sunbeams
• Sunburst
• Volumetric lighting (used by the computer graphics industry)
• God rays (used by the computer graphics industry)
• Fingers of God

(Some links and references in the article.)

As you mention, a singular shaft of light, whether separated from the rest of the sunlight by clouds, annulus (man-made or natural) or through the canopy of a forest is more properly called a sunbeam (Merriam-Webster).

a ray of sunlight

As Andrew Leach mentions and fully explains in his answer, there is precedent for calling this a sheaf or sheafs (or sheaves).

6.
a. Physics and Math. A bundle of rays, lines, etc. all passing through a given point.

But this has two drawbacks with regards to your question.

1. It is a fairly technical definition and not commonly understood in every day English.
2. You would still have to specify what makes up the sheaf; it cannot be used as a single word in the sense you want.

Incorrect

Walking through the forest, I was awestruck by the beauty of a sheaf.

Correct

Walking through the forest, I was awestruck by a beautiful sheaf of sunlight.

There does not appear to be an exact word for sunlight filtered specifically through foliage.

There is a phrase dappled sunlight (or dappled light) that refers to the phenomenon.

Dappled means

marked with small spots or patches contrasting with the background

There are a number of images referred to as dappled sunlight here

Is there a specific, single word in English that means precisely that?

No.

“Sunshine filtering through leaves” is perfectly good English, and seems to be the only exact English equivalent for the phrase you quote.