Can it ever be acceptable to use singular “they” with a specific referent of known but undisclosed gender?

I am not sure whether these two examples using singular they to refer to a specific, singular referent are acceptable in educated speech:

1. I had a friend in Paris, and they had to visit the doctor for a month.
   
   Here, they refers to a friend in Paris, so clearly a person well-known to the speaker and so of determinate gender.

2. A teacher asked me to give their book to John.
   
   Here, their refers to a teacher of the speaker’s acquaintance, presumably also therefore of known gender.

Specifically, I’d like to know whether there’s any difference in acceptability between how speakers of American English view such usage compared with how speakers of British English view this.

Does the Atlantic change how this comes across, or doesn’t it?

(editorial additions for broader linguistic and sociolinguistic focus)

Does one side of the Atlantic Ocean find it pretty normal for educated speakers to use grammar like this, but the other side of the Atlantic Ocean finds it abnormal in educated speech?

Or does — if you would — the “Atlanticity” of locale have less importance on its acceptability than the register being used has, such as the varying registers of casual language versus formal language, or of the spoken language versus the written one, or of spontaneous dialogue versus curated text meant for an educated readership?

Might the acceptability of usage vary more by other factors than locale or register, such as by gender or age or education or class?

Has this usage’s acceptability or unacceptability remained relatively constant over time, or have we seen shifts in that? If so, are these shifts ones of centuries or of generations, or are they quicker than that, perhaps of decades or even of years?

Solution 1:

In a comment, Janus Bahs Jacquet wrote that:

[Y]our phrasing makes it sound like a) you’re deliberately going out of your way not to disclose the person’s gender, or b) you know and respect that they is the person’s preferred pronoun. Both cases are definitely marked, though. This way of phrasing things would never be seen as neutral or unmarked in most contexts.

The default and unmarked way of referring to people you know (and whose gender you can therefore also be assumed to know) is by gendered pronouns, since they are used by the vast majority of the population.

Solution 2:

If I am telling a story about a friend that the other person doesn't know, and their gender is irrelevant to the story, I will use "they"/"them" to refer to them. If it becomes awkward (as it often does if the story is long), I will switch to using their name and the appropriate gendered pronoun for them.

I speak Australian English, and I've spoken to many British and American people without anyone seeming confused or commenting on my use of "they"/"them" for my friend, or later switching to a gendered pronoun.

Gender irrelevant story:

I have a friend who moved to Brisbane. They sent me a picture of the cat where they are house-sitting.

Gender relevant story:

I have a friend who was accused of sexual harassment. He wanted to cheer up a female colleague who was looking a bit down so he tried giving her a gentle bump with his shoulder. Unfortunately, they were in a lift at the time and it lurched, throwing him into her.