In Israel I'm more likely to say "מה" (Mah? literally "what") than "הא" "Huh".

I catch myself when in the U.S. saying "Mah?" to English speakers.

But "huh" exists, as does "ok" (though people are just as likely to say "בסדר" (b'seder).

It's interesting reading about the history of "ok" -- a very modern word with a traceable origin -- that now exists in all languages. Read Metcalf's book:

https://www.amazon.com/OK-Improbable-Story-Americas-Greatest...

This is how the word "OK" started out; it was a joke abbreviation of "all correct": Oll Korrect. You never know when a joke is going to take over the world...

[0] http://www.amazon.com/OK-Improbable-Story-Americas-Greatest/...