One of my students works creating subtitles for whatever television shows and movies come her way. Sometimes she works with bad B-movies (or worse) which go straight to DVD and are of extremely dubious quality. At others, she works with American television shows or documentaries. In her most recent lesson, she was working on subtitles for an episode of a BBC series for the first time.
My job when working with her is to take the parts of the script which she can't understand due to the obscurity of the reference or the cultural connotations. In most cases, this isn't much of a problem for me. However, dealing with a British-made show brings more challenges to the experience as there ultimately are references to things I'm not familiar with like the names of specific establishments that have not been popularized in America (or Japan). As one example, I can say that before this lesson, I'd never heard of "The Baron of Beef."
I'm actually quite a great fan of British television and these days spend more hours watching British drama than American thanks in large part to the Mystery Channel (for which, not so coincidentally, my student was subtitling the show we discussed) and the fact that I'm not keen on much current American drama aside from House and Lost. I'm particularly keen on A Touch of Frost (which I recommend strongly to anyone who can find it in their T.V. listings) and Poirot, though both of these are rather old now. It does take awhile for things to make their way to Japan from any country.
Despite a fair amount of viewing experience with both drama and comedy made in England, I can't say that I'm very well-versed in some of the jokes and their references. At times, the only thing I can do is guess then turn to Google during the lesson to confirm my suspicion. I'd say I'm correct about 90% of the time. For instance, I'm still not sure why someone would say "hello, sailor" when encountering a drowned dead body in the water except that being in the water is connected with sailing. My only exposure to the phrase "hello, sailor" has been through Monty Python and the context for the joke was quite different.
I think my students figure that we all speak English so we all understand anything said in English, but there are clear cultural differences. Actually, I'm pretty sure my British friends wouldn't even agree that "we all speak English" in regards to Americans. If you watch enough of another country's popular media, you can start to see some of the threads which commonly run through their collective consciousness to which they can relate and to which you may not. One of the biggest examples of this that I've noticed is that Oscar Wilde's life or quotes make an appearance far more often in British shows than an American might expect. He was mentioned in the crime drama I just saw a bit of in my students's lesson and also in The Thin Blue Line which I saw last week (and, of course, is in a Monty Python sketch and mentioned in Black Adder). I'm not sure that I've ever heard him mentioned or quoted in an American show except obliquely as a reference to The Picture of Dorian Gray. I imagine similar references to politicians and presidential peccadilloes which run through many U.S. shows in particular may be a little obtuse for some.
In Japanese job advertisements for teachers, some schools will request a "North American native English speaker" or a "British native English speaker" and this can get feathers ruffled amongst those who want to apply for the job and don't fit this seemingly arbitrary criteria. While I'll grant that some of these preferences are a bit frivolous, I can also see where sometimes a particular person or group of people may be better served by someone who grew up in one particular cultural environment or another. In the case of my student and for this one lesson, she may have been served a little better by a British teacher, but only this one time. ;-)