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Being a non-English native, I'm surprised when I read people who use a plural form when they're clearly talking about a single person.
Here are two excerpts from a software I used to work on, written by a former Irish co-worker:
... a supervisor must assign it to themselves and deal with it.
This supervisor has no restaurants assigned to them.
I would have written the following sentences instead:
... a supervisor must assign it to himself and deal with it.
This supervisor has no restaurants assigned to him.
Is the plural form correct English, and if so, is the plural preferred over the singular form?