The "peckish" idiom commonly means hungry in the UK, not in the US. I'd expect "nibble on" to sound a bit more natural in the UK than in the US, but it'd be understood everywhere I think since it's not idiomatic. You say "everything is hunky-dory" (not "something"). Bowie's album probably popularized that expression worldwide. "I beg your pardon" and "excuse me" can each be used to mean "I didn't hear what you said, please repeat it." Or they can also be used to mean "How dare you say what you just said!". The former will sound more natural in the UK than in the US.

In South Africa all these expressions are commonly used and understood in the English community. My Mom likes to say everything is hunky-dory! [emoji]

In the United States, "I could nibble on something" is completely natural. It's common, but it's not as common as "I could use a bite to eat." So is "I beg your pardon." For example, if I accidentally bumped into someone I'd say "Oh, I'm so sorry. I beg your pardon." "Peckish" is not used in the United States, although most people probably understand it. We would just say "I'm a little hungry," or "I could use a bite to eat" (or "I could nibble on something.") I have never ever ever ever (in sixty-five years!) heard anyone in real life use the expression "hunky-dory." However, it's the kind of expression that might be regional. To me it sounds like something out of the 1930s. The American Heritage dictionary, however, includes it without any comments. Perhaps it has been revived and I'm too out of touch to know it.

Yes! People do use the terms "peckish," "nibble," and "I beg your pardon." However, I have never heard of "hunky-dory."

I have definitely heard of hunk-dory, but it isn't all that common! Here in the south people say that mostly when they are joking around, or being sarcastic when things aren't going good at all!