Ok, you need to see the cultural implications.
Deaf people have to deal with hearing people everyday. They are often treated as inferior because they can not hear, and (often) use a language that is different than the majority. Because of the language barrier, many people look down on Deaf people, think that they are stupid, or incapable. In the past, this view was perpectuated by interpreter or educators, parents, relatives, or even spouses, who "jumped in" and "rescued" Deaf people from interactions with hearing people. Deaf people were not given the opportunity to be independant and self sufficient. Luckily, times are changing. Hopefully, there is more education in the world, and hearing people are starting to see Deaf people as equals. If I had stepped in, I would have validated the idea the the mother couldn't handle the situation for herself (even if the employee didn't know, the Deaf mother would have), and I didn't want to be a part of that.
So, no, French people do not have the same cultural mores that dictate the behavior in this situation, but Deaf people DO. That is why they are considered a linguistical and cultural minority group in the US, and not just people with a disability.