I know circumstances change all of the time but in late May, we did not have to wear a mask on Delta from Detroit to Paris but we did have to wear a mask on Air France from Paris to Barcelona. Same for the flight back. Air France required masks for Barcelona to Paris but no mask required on Air France from Paris to Detroit. We were told it was because of the Spain requirement, not an airline requirement. In Spain mask required on public transportation, including tour buses. Air France handed out masks as you boarded if you were not already wearing one.