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The Teochew variant of Minnan is the main language here, and it is only marginally mutually intelligible with the Amoy/Taiwanese variant. Locals are very proud of their language despite government attempts to standardise Mandarin as a common language, so any attempts to speak Teochew will be met with encouragement, and may even get you preferential treatment in shops and restaurants. As Chaozhou is part of Guangdong province, many people speak Cantonese as a second language. As with elsewhere in mainland China, standard Mandarin is the only language taught in schools so expect all educated people to be fluent in Mandarin. English is not widely spoken, though staff at the higher end hotels will be able to speak English.
Despite many residents having relatives in the much more international city of Hong Kong, non-Chinese vistors are not currently common here so expect some friendly curiosity and attempts at conversation from people if you visit, especially from kids/teenagers who know a little bit of English. However, when shopping or dining you'll be treated the same as if you are a local resident. The city is developing with China's economic expansion, so visitors and facets of western culture, while still infrequent, are becoming more common.