So... maybe we should all just agree that, just as an article I read on the Guardian UK's site said: "unless one casts Indians to play Indians (unlike Alec Guinness in A Passage to India, 1984), Danes to play Danes (instead of accent-prone Meryl Streep's Karen Blixen in Out of Africa, 1985), Irishmen to play Irishmen (to avoid the many begorrah horrors) etc, most accents [in movies] border on caricature," and thus we should just accept that fact, instead of griping every time an actor's/actress's attempt at an unfamiliar accent fails?!
That's as much of a question as it is a statement, by the way.
We've had convos on this blog about the accents of American actors taking on non-American roles (and vice-versa) - for example, Sanaa Lathan in Wonderful World, and Morgan Freeman in Invictus.
Frankly, for most audiences who don't have an ear attuned to the nuances of Senegalese and South African accents (which themselves also vary within those countries) in these 2 cases, Lathan and Freeman (and Matt Damon) will sound authentic enough.
But is "authentic enough" enough? Is the audience being deprived of a proper "education," or are our expectations too high, in expecting perfection of speech from these actors, especially when many of us here likely wouldn't even be able to recognize what's authentic and what's not, in any given situation?
The writer of the article makes a comparison between "blacking-up" and actors in roles that require that they speak in an unfamiliar accent - essentially suggesting that just as black people are now "allowed" to play themselves on screen, instead of white people in black face, "accents should be left to native speakers."
In this industry, it comes down to this: Are there recognizable/bankable English-speaking Xhosa actors, and English-speaking Afrikaner actors to play Mandela and François Pienaar respectively, in Invictus?
I agree that an overall appreciation of a film can indeed be undermined by suspect accents; and what all this calls into discussion is the casting of "natives" in roles like the above I mentioned, instead of American Hollywood stars, if ensuring authenticity is crucial. But then that challenges one significant industry belief: that recognizable names and faces are needed in order to sell a picture - an idea with a lot of support that likely won't falter any time soon.
So, in short, expect more "suspect" accents, especially in Hollywood studio movies centered on stories about non-Americans.
On the reverse, while there have most certainly been exceptions, given how ubiquitous American/Hollywood films are all over the world, as well as music, I'd say that most non-American actors do a pretty good job mimicking North American accents.