Dear Antony
thank you for sharing your experience problem, your knowledge and your expertise.
I understand what's happen in your restaurant because I have been working in the restaurant with my relative at the UK. If staff none speak English and don't understand anything that very difficult to handle. You must take the time with the coaching staff. i know that you know, But it will have problems with the staff, when you teach them to understand the duty, they may resign to work another place any time.