Words like חמץ and kx’āhã don’t appear in English. These words, like thousands of others, include sounds that aren’t part of the normal spoken range of the language. We don’t have difficulty saying or hearing these sounds, they’re simply sounds we have rules against.
The question is: Is the alphabet we use missing those sounds because we don’t use them, or is it that we don’t use those sounds because we don’t have letters for them?
If you can’t see it, you can’t say it. And that goes for more than words.