It is very difficult to give you an example of those differences. Croatian and Serbian are two different languages, like Spanish and Portuguese, or Czech and Slovakian, and although we understand each other very well, there is some difference in grammar (especially ije/je : e). Ije/je is used in Croatian, although some dialects have "e" instead, and "e" is in Serbian. But in Monte Negro, which is a part of Serbia & Monte Negro federation, "ije" is used quite often as well.
As you can see, it's all quite complicated for a person not living here, or not knowing the language, dialects and accents well, and I hope you'll get more answers from my colleagues who will maybe be able to explain it better to you! :-)


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Note added at 3 hrs 2 mins (2005-01-21 12:55:22 GMT)
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Problem u usporedbi s američkim i britanskim engleskim je u tome što su oba službeno engleski jezik, dok su hrvatski i srpski dva zasebna službena jezika pa je usporedba vrlo teška. Možda su španjolski i portugalski bolji primjer gdje se riječi slično, ali ne jednako pišu te različito izgovaraju, a španjolci i portugalci se sasvim dobro razumiju, osobito portugalci španjolce (iako se često prave da se ne razumiju, ali to su već neki drugi razlozi kojima ovdje nije mjesto :-))

I suggest talking to the author if possible to see what solution would be acceptable to her or him. If you do go with the British/Am thing you have the well known difference in pronounciation of things like schedule, tomato, potato, and can get more ideas from articles you can google. The Economist style guide (on their site) covers this a bit too. The challenge is that the author is not using different words, but the same words with a slightly different spelling and pronounciation. The other possibility is contrasting the accents of Southern Americans (with a twang) and Northern Americans (and most others). Whichever choice you go with though, it will not be a perfect solution because this is very difficult to quickly convey to non-linguists. It calls for some extremely creative adaptation, or even circumvention.