Perhaps one of the most enigmatic words to non-speakers of Navajo, wah (or in some cases, wah-hah) is not so much a word as it is an expression.
The English counterpart would probably be “oops” when the speaker is talking about himself/herself. If the speaker is referring to others, it may be more of a jab at their clumsiness or failed attempt at doing something.
In other use cases, elders may exclaim “wah!” (expressed in a more drawn-out fashion) when they sit down after a strenuous activity. It would probably approximate to “whew!” in this instance.