That's why translating them is fun! Coming up with your own is giving up - intellectual laziness.
Everyone who translates for serious purposes (and HPMoR would belong in that category IMO) needs to have read Hofstadter's Le Ton Beau de Marot. He discusses the issues involved at length and with his usual wit and insight.
The point is not to show off how clever you are, it's to make the best possible finished product. The people who need the translation aren't going to be checking how close the jokes are to the original material. They're going to care how funny the jokes are.
We're currently translating chapter 11 into German. It's going along fine, but
is still puzzling us. No dictionary entries, no HPMoR-unrelated search hits, nothing…
Is this some kind of dadaist joke by Eliezer? Or are we missing something?