"'Iw bIQtIqDaq jIjaH."
Translation:I travel the river of blood.
Yes. It is an idiom and that is the standard translation of the Klingon sentence. leng would be a great way to translate the English sentence into Klingon and it is accepted as a possible answer on the exercise in that direction. "Go" is also accepted as a translation in exercises of this Klingon sentence.
It's not an idiom, it's a metaphor. An idiom is a saying where the words don't mean what they say (e.g., a "piece of cake" has nothing to do with cake); a metaphor is where you describe one thing as a stand-in for another thing. There's some overlap, but this sentence happens to mean exactly what it says, even if it's only a metaphor.
The reason jaH is being used where the English has travel is because Marc Okrand isn't quite so strict with literal translations as you'll find on this site, and Okrand translated this sentence (it comes from the episode "The Icarus Factor").
Adding to the discussion that's already happened here, since I was pondering around this one too, I think it might help to consider that -Daq can be translated as to, on, at, in, etc. So I think "upon" might also be valid, so in the case of this sentence I think "I go upon the river of blood" helps better parse the translation, because the expression, as I understand it, refers more to traveling "upon" the metaphorical river of blood, than "to" it.
The phrase travel the river means travel on or upon the river, not in it. I'm sure you could say travel the river if you were in a submarine, but the point of the phrase is that you follow the course of the river, and not on the banks. Typically, this means a boat. Consider also travel down the river and travel up the river.
The gauntlet may indeed represent the River of Blood, but that doesn't mean Worf is represented as swimming or wading in the blood. I mean, it's not impossible, but there's nothing there to particularly lend itself to that interpretation. It's all too symbolic and abstract for that.
My impression of the ceremony has always been that the River of Blood is a symbolic representation of one's journey through life and all the travails therein. The Klingon must endure and overcome them to be considered complete. I always figured the blood referred to is Worf's own blood and the blood (and other bodily fluids, representative of achievement) of his enemies. Traveling the River of Blood is journeying through life, which generates all that blood.
I disagree. I have no problem interpreting travel the river as meaning wading along the river or even swimming along the river. Traveling up or down river by wading or swimming seems to be fine by me.
Since we aren't given any sort of concrete meaning, I'm sure we can all have our own interpretations of the metaphor (both the phrase and the location) and it will still work just as well.