Is there a specific reason why 'worked' wasn't accepted? Is the Welsh imperfect literally for these "I was ...ing" constructions or can it also be an undefined past action?
For 'I worked' we would use the short past tense, ie gweithiais i or mi wnes i weithio. Although I can see what you mean. Yes, on reflection it could be equivalent to 'I worked' in English, so I'll add it now.
Isn't every cafe private, except in a communist country? They all are in Wales.
It's not a euphemism but it refers to the sort of café you'd get in a company/office/factory which was only open to the staff and not the general public.