* deciding if singular or plural is relevant based on the antecedent.

* deciding if singular or plural is relevant based on other context.

* deciding if the singular or plural actually meaninfully changes the meaning of the statement within it's context and not worrying about if it doesn't.

* in the vanishingly rare cases where it's meaningful, contextually unclear, and I am still unsure, I can ask.

I may be an imbecile, but fortunately it takes only a minuscule amount of mental power to handle all this. English has a lot of redundancies and deducing from context is built into the language.

So when hear a simple snippet "they are foreign" I assume either it will become clear from further context, or it doesn't matter how many people "they" refers to since someone is having a tantrum about pronoun usage.

Perhaps what's really bothering you isn't that I pointed out the historicity of a common, centuries-old pattern in the English language, but rather that someone missed naptime and is grumpy.

This is almost never ambiguous within context. I blame the outrage on illiteracy. If you don't read a lot, even a simple turn of phrase or grammatical ambiguity could be anxiety inducing.