Most of the people in the fashion industry in China will most likely know how to speak one of the three languages you mentioned. Since they have to deal with international models and agents communication is a key to their success so it shouldn't be that hard. I know many people that speak at least English. If you ever run across someone who can't  speak one of the languages you mentioned you could always hire a translator or get someone to help you communicate with those that can't communicate with you directly.  

whoa almost a decent response there from mattaya.....
He is right in that many people within the fashion industry here in china will speak one of those languages if not more. At the very basic level you might be of use to a company simply because you speak those languages... but that might not be in Shanghai.
As for finding a job, i cant really comment on Shanghai, but here in guangdong where all the textile and shoe factories are, the majority of foreign employees are brought here by their companies, i.e they get the job in their own country and are sent out here to work with developers and designers. You can try to just turn up and look for a job but i think it will be more tough.

i think it is not diffiuct as long as you can speak english. i find some companies on this net to find fashion designer. you can put you resume on the net. i think you will get very good job soon.

most of young chinese can speak english .so that would be not a problem