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Answers: Language:Mandarin
Mandarin:is a category of related Chinese dialects spoken across most of northern and south-western China. When taken as a separate language, as is often done in academic literature, the Mandarin dialects have more speakers than any other language.

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It is completely in Mandarin Chinese

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It was filmed in Mandarin, Directed by Ang Lee and starring Tony Leung (who has previously won Best Actor at Cannes).

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As the other respondents have pointed out, the movie is in Mandarin. Since there are scenes shot in Hong Kong and Shanghai, I presume there would also be dialogues in Cantonese and Shanghainese. Apparently, Tony Leung, a Cantonese-speaker from Hong Kong, had to undergo intensive Mandarin training in order to do this movie. He jokingly said in one of his interviews with the Chinese press that since he had to memorize the script in Mandarin, his most dreaded scenario was Ang Lee deciding suddenly to change major parts of the dialogue, since it would have meant more memorizing in a dialect not of his own.

Contrary to the opinion offered by one of the respondents, Mandarin is originally the dialect only in Beijing and surrounding areas. Due to the fact that the official elite ruled from Beijing for a long period of time, Mandarin was picked by governments in the modern period to be the official language. There are many dialects in China, most of which are very different from Mandarin. If you have travelled across China, you would have noticed that actually, many older Chinese people do not necessarily speak Mandarin that well, and even younger people speak Mandarin tinged with accents from their own dialects.

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