It's the mother tongue there, mate. You decide how important it is. And don't believe the quip that most Chinese speak English. They don't.

You'd better learn some chinese before you go there.

Most Chinese can speak English,you don't need to worry!

学一点官方语言很有必要，中国各地区地方方言很多，发音也不一样，我个人建议你先学普通话

You don't need to speak chinese when you are newly over here because you don't speak it. but then again, if you have learnt to say 'ni3hao3'( hello) and 'xie4xie4'( thank you) it will help to make yourself welcome. You may ‘speak' sign language to people here. Over the days you live here, you will learn to speak chinese bit by bit, and improve quicker and quicker, because you have had the best teacher: the Chinense language environment. By the way, people in Jiaxing speak a very beautiful dialect, which is greatly different from Mandarin, but almost everybody today speak (or at least understand) madarin. So you'll learn both the languages without doubling your effort.