Actually, using "they" or "them", while commonly done on the internet, is NOT grammatically incorrect. Correctly, it should be he/she or him/her. But it looks awkward, and people don't like doing it, so they usually use "them" when they want to hide the gender of a character in a story, or when they don't know the gender of an individual. But because "they" and "them" is plural. It is NOT correct. Ever.
"It" would be more correct or, as used to be commonly done, using "one". Because the site was translated from German to English for those of us who speak English, "one" wouldn't have been considered. (I don't think any non-English languages use it.) But here's an example.
When leaving the house, one puts on shoes.
That's a sentence where you don't know the gender of the individual, or where the gender is irrelevant. But very few English speakers know about this rule, so very few do it.
Yes, I am VERY picky about my own grammar and I notice whenever people use it incorrectly, although I rarely correct others because it can seem rude and insulting to do so all the time. (Don't get me started on when "less" and "fewer" should be used, or the various "lay", "lie", "lain", etc. And the confusion between "lose" and "loose" or "lightning" and "lightening"! Those are amongst my pet peeves!)
And it actually is perfectly acceptable, even in English, to use the male pronoun when gender is unknown. It's leftover from when the society was patriarchal and misogynist. 