https://dictionary.cambridge.org/grammar/british-grammar/a-a...
https://dictionary.cambridge.org/grammar/british-grammar/a-a...
There are all kinds of cases where this reveals interesting things about how someone pronounces things.
An American will speak of “an herb” because the h is still silent there (“an ’erb”), whereas an Australian (and most other English dialects) will speak of “a herb” because it’s no longer silent.
In the KJV, 1 Kings 10:29 gets two in one verse, speaking of “an horse for an hundred and fifty”, showing that in the English of the early 1600s, you had “an ’orse” and “an ’undred” by pronunciation, whereas all major dialects now sound the h. (For reading aloud, I personally say “a horse for a hundred and fifty”, having decided that a/an are the same word just with context-dependent spelling and pronunciation, like “the” has two context-dependent pronunciations (“thuh dog” versus “thee elephant”, likewise based on the next syllable’s sound), though they’re both spelled the same way.)
If a Rust developer writes “an &str”, they’re probably pronouncing it “an ampersand str” or “an and str”, but if they write “a &str”, they might be pronouncing it “a str slice” or “a reference to a str”.
I don't know what I'd call (or you're calling) 'major dialects' (just RP & GenAm?) but quite large geographic chunks of England would say "an 'orse for a 'undred", in the early 2000s.
(And 'a undred' is not a typo. I don't know why that's different, but 'an undred' just sounds wrong to me.)
I should also note that Indian English is also a bit patchy, their leading aitches are regularly silent due to it not being a common construct in their own languages; but they’re also less precise about a/an in general too.
I'm British, so I'm not that familiar with many American accents, certainly not your examples, but off the top of my head you do find elongated vowels, t->d, ay->i (short), rhotic r, nasalisation, 'vocal fry', 'baby voice', and ending every sentence or half sentence with rising intonation like it's a question?
Yorkshire doesn't pronounce the aitches.