7and8

I was told once that (especailly with the French) you should ask them in their own language if they speak English. The sentiment being that you try to seem like you deserve to be there. If done properly, they may not know you are American.

This is such crap. Firstly, I think we are the only culture that wears Tenni-shoes as casual fashion. Nothing wrong with that but it makes us detectable. Mainly speaking for the men (because there is nothing I understand about the woman/shoe relationship). Euromen wear leather shoes. They maybe the trendy retro puma / bowling style or loafers or loafers with buckles or dress shoes they also use while they paint the house. If you don't want to stand out as a Yank, change your shoes.
Secondly, if you carry yourself respectfully and look for someone who is used to taking care of those unable to take care (someone who makes a living from tourists, a parent, a beer museum curator tired of dealing with giggling college boys) of themselves then your query will be treated as such.
Lastly, Stop it. Don't try to blend in just enjoy the surroundings.

In an unrealated story:
There was a group of teenage tarts coming back from their trip. They agreed it was good to be back in the states. They were sad, however, that they wouldn't be able to talk candidly about someone in front of them as everyone here speaks English. Dear Tarts: Ours is a country globally involved yet consistantly knows only one language. Besides they could see you coming by your Ambercrombie "shirt" and Reeboks.