Yes, it varies from country to country.
According to ICAO SARPS (Annex 6):
"An operator shall establish, to the satisfaction of the State of the Operator, the minimum number of cabin crew required for each type of aeroplane, based on the seating capacity or the number of passengers, in order to effect a safe and expeditious evacuation of the aeroplane and the necessary functions to be performed in an emergency or a situation requiring emergency evacuation."