The interesting part of that to me, too, is how many of them roundabout derive from eras where erudite and highly educated English speakers were forced to learn Latin as well, and in so doing apply Latin grammar rules to English that don't apply to natural English. The most obvious example being "never end a sentence with a preposition", which is a very clear grammar violation in Latin, but natural English has ended sentences with prepositions for a very long time.
To a lesser extent I think it is also Latin education's fault why the "objective" case continues to linger in English, despite being so mostly dead, as it acts as an education marker. `Whom` is a zombie only insisted upon by certain educations and should just be buried and put out of its misery. The confusion around `me` versus `I` and which scenarios to use which probably will only get worse.
"never end a sentence with a preposition" is not a grammatical feature of English (from a scientific perspective where "English" is what we observe as being spoken by the community of native speakers, as opposed to something grammar books invented), and does not serve to distinguish native from non-native English speakers, at all.
I don't think this was the sort of thing GP was thinking of.
Edit: I didn't even intend for the previous sentence to be an example of a native English speaker producing sentences that end with prepositions, but by happy coincidence it is.
There are still teachers today that teach "never end a sentence with a preposition" in a long chain game to some early English grammarians that tried to reapply the rule from Latin back onto English (to every native speaker's chagrin). It still impacts the way that many people write. Much of English "formal writing" still tends to soft require the rule and definitely in writing it can be used to distinguish someone that learned English writing rules in a formal educational setting versus those that did not. It very rarely filters into a way to distinguish someone's speech, but it's still a very living distinguishing characteristic in writing.
> it can be used to distinguish someone that learned English writing rules in a formal educational setting versus those that did not.
Sure, this might be true, and I'm aware that it's what you meant, but it's not the same as being a way to distinguish native from non-native speakers (or even writers).
Many, many non-native speakers got to quite advanced levels of formal English writing via formal schooling, especially in places like Northern Europe. I suspect people like that are actually more likely to avoid ending sentences with propositions than native speakers are.
I think what the person who started this sub-thread was referring to is stuff that really is intuitive for every cognitively normal native speaker, like the difference in meaning between "the dog bit the man" and "a dog bit the man". Practically every native speaker, including illiterates, would agree on whether "the", "a"/"an", or no article at all is correct in any given situation, whereas it's very difficult for many even highly educated non-native learners.
English merged accusative and dative centuries ago as it dropped most other cases, and this merged almost-a-case is generally called the "objective case" by English grammarians. Though the more accurate from the point of view of Latin grammarians name for the case is that English has an "oblique case".
English doesn't have an accusative or dative case. There are a few different names for the two different cases of English pronouns; "nominative" (I/he/she) vs. "oblique" (me/him/her) and "subjective" vs. "objective" are both reasonably common.
From Wikipedia:
> An objective case is marked on the English personal pronouns and as such serves the role of the accusative and dative cases that other Indo-European languages employ.
To a lesser extent I think it is also Latin education's fault why the "objective" case continues to linger in English, despite being so mostly dead, as it acts as an education marker. `Whom` is a zombie only insisted upon by certain educations and should just be buried and put out of its misery. The confusion around `me` versus `I` and which scenarios to use which probably will only get worse.