How should one translate "祝你年年有今日，歲歲有今朝" into English?
Both "年年有今日" and "歲歲有今朝" have the meaning of "May you have today's glory forever."

Usually it's wished upon people on their birthdays. The contextual meaning is "Although you are getting older as years pass by, I wish that you'll always have today's glory. And let today's good memory always be with you."

It is not used by a particular group. Other similar expressions include "祝你青春永驻", which means "may you have your youth forever".