Writing dialogue is

difficult for an author. Jane, of "How Publishing Really Works", raised the issue in her blog this morning. I added a comment that, apart from the nature of spoken language itself, there are also cultural and generational differences that make it difficult.
Oddly this came up yesterday. I met the Knitting Gang for a little R and R and we discussed everything as usual. I think we are unusual for a group of women. We don't bitch. It's an unspoken rule but it is there nevertheless. The group includes an Italian, two English women, a Kiwi and others. We are a mixed bunch. We did have two Americans. One has had to return to the US and we miss her greatly. She is married to a Frenchman, has lived in Russia and France and understands that cultural differences exist even better than the rest of us. The other American no longer comes. Her personality simply does not allow for cultural differences. She clashed because she misinterpreted words.
Of course there are words that cannot be interpreted. There are words that do not have parallels in other languages. We all have an unique understanding of language as well. My idea of 'chair' is not your idea of 'chair' - even when we both experience sitting on the same chair. My idea of 'chair' has changed from yesterday and my experience of yet another new chair.
Perhaps this is why another American friend no longer tries to read current British crime fiction. It is clear that she does not understand the dialogue, not just the surface dialogue but the sub-dialogue. She cannot understand the underlying meaning of the words.