I think it depends on the setting. If the setting is France and the languuage being spoken is English, then they should just use their natural accents. A french accent would be cheezy in this situation. However, if an American actor is playing a French person speaking English, then they should use a French accent. Or something to that effect. They are actors after all, aren't they? Let's see some acting. I don't want to see them act like themselves.
Here are some bad examples of what I'm talking about:
- Leonardo DiCaprio in The Man in the Iron Mask
- Kevin Costner in Robin Hood: Prince of Thieves
I was embarassed at how poorly they did these roles. It was almost comical to hear their plane old American accents.
- Kevin Kline in French Kiss
- Gwyenth Paltrow in Possession.
I hope I'm making sense...