DUBAI, United Arab Emirates—When Khulud Abu-Homos, a television producer at OSN network here, decided to dub the Harry Potter movies into Arabic for distribution in the Middle East, she faced a quandary: which Arabic?

The Arab world, it turns out, isn't one world at all. It's a collection of overlapping worlds that harbor a dizzying array of diverse people, cultures and language. The rest of the world noticed this recently in the varied ways the Arab Spring democracy movements have played out.

Ms. Abu-Homos knew the choice of Arabic dialect was critical if Harry Potter's charms were to find a place in the hearts of Middle Eastern television viewers—or to turn out to be a flop. "You don't want to go wrong," she said. "Instead of attracting people, you can turn them off."

As the Arab world consumes more films and television shows from beyond the Middle East than ever before, dialect has become a critical tool in the regional battle for some 250 million Arab viewers. For the month of Ramadan, a four-week stretch that falls in August this year, broadcasters gear up for months, producing their best series, and advertisers concentrate media buys during the weeks.

That means putting a lot of thought and effort into dubbing.