Crew members are very literate in their own launguages. English is one of the most difficult languages to learn. There are groups of on ship employees that are not required to speak English, especially those that do do interact with passengers: laundry workers, Deck and Engine Personnel for two. If an staff members deals with passengers, they have to speak English. At one time there were English classes available for crew members.
To answer your question, I was 14 when I go my first real paycheck and NO I did not know about deductions for taxes, insurance, social Security, etc.