[deadwing0]

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).

[hashmush]

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".