Starbucks is expensive. Probably more than a regular coffee at a regular French cafe. If french from all nations prefer to have more expensive coffee at starbucks than at their local vendor this just shows how badly the local vendors need to start to get back to work. Not that a regulation is needed to protect them from better competition. This might work in the short run, but it long term lack of exposure to competition will just make them weaker than they already are.

And there is another, moral hazard kind of a point: Why would you like to force people to buy something they perceive as worse? You are right they worked hard to get this money and this is not your or Government business how they spend it.