Re: I am just curious what Google uses for "Trash" for UK English? Rubbish?
"Bin".
And I've had reports of Gmail changing US <-> UK English seemingly on its own.
Re: I wonder why they did not go a different route: At the server database, keep the folder/label name the same, in English, but at the level of the client (webclient, mobile app, ..) - map according to the locale.
Beats me.
That's what most other mail services do.
And IMAP has "hints" which tell you which is which (drafts, sent, deleted, etc.) so a client won't have to guess.