I quite agree with Abdul (writing in response to my post on Afghanistan, 18 June 2007) that no one can be expected to know the “correct” pronunciation of every name. That is why the BBC has its Pronunciation Research Unit, which is dedicated to finding out the native pronunciation of any name (or indeed any word) that they are asked for, and then to provide a version to broadcasters that is acceptable to a native speaker but at the same time not too difficult for an English speaker to reproduce. Abdul also makes the point that familiar, well-integrated names such as Paris have their established anglicisation. How long, for Abdul, is long enough? Afghanistan has been a familiar name in English since at least the middle of the 19th century, and the pronunciation given in the English Pronouncing Dictionary since at least 1932 (the earliest edition I have to hand) shows [g] as the first consonant of the second syllable. No native (and which native language from that troubled country should we choose?) language version is given. Afghans do not speak Arabic, so the sounds of Arabic are irrelevant in any case, introducing yet a third language into the mix.
The question of whether English has a voiced velar fricative is one for phoneticians to argue over. No naive English speaker would recognise the sound as one they use. Marginal allophones cannot be used in this way. Most English speakers use both a clear and a dark /l/, but they would be unable to produce the “wrong” one without training. The former Conservative leader Michael Howard, whose Welsh accent leads him to use a clear [l] in syllable-final position, was pilloried mercilessly by comedians for this trait.