The same happens with animal noises. The sound is the same, just different languages write it down differently. For instance, English "woof woof!" and Polish "hau hau!" look completely different, but there is an overlap in possible pronunciations, and that point of overlap actually does resemble the sound dogs make.
"Ouch" is what you say to express that you imagine something hurt, what people actually say is more like "ow" or "argh".