China

Standard Chinese or Mandarin (Putonghua, based on the Beijing dialect), Yue (Cantonese), Wu (Shanghaiese), Minbei (Fuzhou), Minnan (Hokkien-Taiwanese), Xiang, Gan, Hakka dialects and other minority languages.

The official language of the PRC is "Putonghua", a literal translation of which is "common speech". This is known in English as Mandarin Chinese. However, this somewhat misrepresents the true picture. According to Chinese government figures, only 53% of the population speak putonghua. Also, Ethnologue lists more than 200 languages in use in China and there are countless local dialects. This can be a problem, not only for the poor foreigners struggling to communicate, but also for the Chinese. It not unusual to see two Chinese struggling to understand each other.
The saving grace is that the majority of these dialects have a common written form. The pronunciation of any character can be completely different in say, Beijing from that in Guangzhou (where Cantonese is the dominant language), but the character looks the same. For that reason, nearly all television programmes are subtitled and the Chinese often communicate by passing notes. This can be doubly frustrating for us. After struggling to make himself understood verbally, the new Chinese friend you have just met on the train will hand you a note in a Chinese scrawl, utterly sure that he has solved the problem.
That said, the majority of people you meet will speak or understand Putonghua. It really is worth making the effort to learn even a little. You will gain a much better insight to the lives of Chinese people.
For teachers, another, often overlooked, advantage to learning even a little Chinese is that it can give you a much better understanding of the difficulties your students have with English and therefore improve your teaching. For example, Chinese do not have a tense system like English, relying on time adverbs much of the time. So, when your students say "I tomorrow go Beijing", they are using Chinese grammar with English vocabulary. I spent some time teaching a group of students who had between them a number of different 'mother tongues'. After a while, I was able to identify which were which by the mistakes they made in English pronunciation. The differing languages each had different interference patterns.

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