First of all, for the most part I’m not counting anything in bolded. Grammar trip ups or using weird words are very likely disqualifying, in nearly all cases (I can come up with some exceptions, but we would be straying farther from the derail). So I for the most part agree that anyone in the bolded wouldn’t count as a native speaker.
The only people I’m giving a pass to is those who speak it perfectly in every way, but they just have a different accent.
I guess Japanese is different in that there are a probably a lot more extremely different English accents than there are Japanese ones.
For example, I think that it wouldn’t take me that long to be able to learn a decent Australian accent, for example. Actors do this pretty routinely for parts all the time. Obviously you would have to do more work than that, but it’s still achievable. However, there’s no point to doing it. Similarly, someone who can speak perfect English but with an accent could probably do the same thing and learn an American accent if they so chose. Most people just don’t because there is no point if they are perfectly understood anyway.
The other problem with your definition is that it would create a problem for people who speak only Japanese, but have a weird accent. This happens infrequently, but I encounter it in English and I presume it must happen in Japanese at least rarely. Sometimes they have a reason for it (e.g. speech impediment) but other times there is no discernable reason. It’s just how they talk and it doesn’t sound quite like any known accent.
They would by definition have to be native speakers, but if most other speakers think their accent is weird, then that makes them not native? Seems like we end up in a paradox that can’t be resolved.
Yeah, that is true depending on the language, which is why I said it would take an “insane” amount of effort. But most languages have a bit of a range in what’s acceptable for various sounds (English may be an outliar here as far as number of variations). Also as mentioned above there are rare people who speak only one language and still have a weird accent for some reason. It would make no sense to call those people not native speakers.
At the end of the day, I think this is mostly a lot of edge case nittery. I’d say if you truly are perfectly fluent (at least by my definition) you can probably fix the accent with a lot of effort. But if you’re that good at the language, there is really no point unless you are an actor or something like that.
It means Jamie Lee Curtis is almost guaranteed to go two for two as a nominee for a best supporting category, with a strong shot at coming in as a winner the second time too.