Brigitte D. asks
“Which is correct, ‘headquarters or ‘headquarter’ as the administrative centre of a company? I have seen both forms used and would like to know which I should use.”
The administrative centre of a company (‘Hauptsitz’) is always ‘headquarters’. Admittedly, this looks like a plural noun. But ‘headquarters’ can be treated as a singular or plural. So you can say ‘Our headquarters is located in Paris’, or ‘Our headquarters are located in Paris’.
The word ‘headquarter’ only exists as a verb. The UNO is going to headquarter itself in Bonn. UNESCO is headquartered in Paris.
Unfortunately, a lot of German and Swiss firms incorrectly use ‘headquarter’ as a noun. Don’t let them irritate you.