I'd expect many more words to exist in all languages. It would seem that there is a core set of words that are absolutely fundamental to any sort of spoken communication (yes/no, for example), and would be very surprised if this word "huh" is the only one so far found to exist in all languages.
In some situations, yes, but you can say yes and no. 是 (shì, roughly translates to "is" in most situations) and 不是 (bú shì, no is). It's definitely not as cut and dry as the English yes and no, and it gives Chinese kids hell when they're learning English (I taught there for 6 years).
Definitely and to add to that, to my understanding (better than basic, far from fluent), 是 is more of a fallback verb following the same pattern than it is a translation of "yes".
