Within UK dialect there would be some significant differences in many of these words, even ignoring the meddle/mettle examples - farrow/pharaoh is easily distinguishable, too.
I would say, though, that to people _outside_ the dialect, there may be many more words that are indistinguishable. Listening to Scots speakers requires a lot more effort for me because to my ears, many of the differences in the words are extremely subtle.
I agree it's heavily accent dependent and I suspect the original compiler wasn't that aware of non-mainstream US accents.
It's interesting that many of these are only the same (initially at least) if you've been sloppy/ignorant in your pronunciation and then those become baked in ways of saying something.
We're due to get a lot more of these given how often you hear influencers guessing at what to me seem fairly mainstream pronunciations!
These are often a way that TTS systems slip up most obviously. A lockdown project I tinkered with several years back was a small (traditional) LM that had been fed with tagged examples and could thus predict fairly well the best sense for a particular case. It made a huge difference to perceived quality. Now of course, many TTS cope with this fairly well but you still hear the off slip up!
"farrow"/"pharaoh" is more than easily distnguishable - to me, the first vowel in these are nowhere even close to the same - I use "a" from "apple" for "farrow" and "ai" from "air" for pharoah, along with a contrast in vowel lengths, again like "apple" and "air".
EDIT: interesting grammar note - as a native speaker, I can't even decide if that should be "first vowel in these is" or "first vowels in these are" or what I actually wrote above which is what seems more natural to me, although immediately stood out to me as grammatically inconsistent when I re-read it after posting...
> as a native speaker, I can't even decide if that should be "first vowel in these is" or "first vowels in these are" or what I actually wrote above which is what seems more natural to me, although immediately stood out to me as grammatically inconsistent when I re-read it after posting...
I would say that the former (“first vowel in these is”) is ‘more correct’, but it sounds weird because it contains the plural “these” immediately before the singular “is”. What you actually wrote is inconsistent strictly speaking, but it feels better because the verb agrees with the immediately preceding word. (This kind of thing is rather common in languages with agreement.)
I would say, though, that to people _outside_ the dialect, there may be many more words that are indistinguishable. Listening to Scots speakers requires a lot more effort for me because to my ears, many of the differences in the words are extremely subtle.