Japanese onomatopoeia is incredibly cool. But if you don't already know, can you figure out which of the 2 words above is supposed to sound like "many small things gathered together and moving, such as a swarm of insects or a crowd of people seen from a distance" and which is supposed to sound like "doing something difficult on purpose, even though there is no need to, such as swimming across a river instead of taking the bridge"?
I'm glad there are words for these things at all, whether they seem truly onomatopoetic or not. Let's just adopt the Japanese words. No need to anglicize. This isn't like the way there are endless versions of how a dog bark or a cock's crow gets transliterated in different languages. People knew they needed those words before they noticed that other languages spelled the sound differently. The Japanese originated the desire for words that sounded like many small things moving together and doing something difficult but unnecessary on purpose. We see their words at the same time we first think we want such words, so waza waza and uja uja it is.