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As for the translation of Cannes, 坎城 is the official translation in Taiwan. At least most of the media use this term. However, 戛纳 or 加纳 are also used recently, only recently.
戛纳 is used in Mainland. We’ve heard people either pronounce gānà or jiānà. Actually, the correct pronunciation of character 戛 is jiá. However, it’s a relatively uncommon character so people don’t really know the “correct” pronunciation. Moreover, it looks very similar to another character 嘎gā. People would naturally try to pronounce gā when they see 戛. Since 戛 and 嘎 are both onomatopoeia (象声词), we are not that strict to the pronunciation.
In this lesson, we say gānà because it sound closer to the original sound of Cannes and it’s been used in real life.
Hope you find this helpful. 