But that's just my point, it's not arbitrary when it comes to measurements, because they're different things. A kellicam is different from a kilometer is different from a mile. I mean, is it arbitrary to translate references to cubits in the Bible rather than converting them to feet or meters? Of course not, because it's a distinct unit. It has a different length than a foot or a meter.
Besides, one could argue that "kellicam" is the English word for the unit that's known as qelI'qam in Klingonese. In fact, that's exactly what Marc Okrand says in The Klingon Dictionary. Look up qelI'qam and it gives the English equivalent as "kellicam." However you spell or pronounce it, it's a distinct unit of a specific size. Substituting "kilometers" for "kellicams" would make as much sense as substituting "purple" for "blue."
But if none of your readers know what a kellicam
is, all you've done is confuse them. And obviously you wouldn't do a one-to-one substitution of "kilometer" for kellicam
. But you could approximate.
Or, you could take the Forged in Fire
approach: "Koloth saw that the enemy ship was 17,000 kellicams
away, or, as the Earthers would say, 32,743 kilometers."