After you download Oracle SQL developer 2.1,you will find it's all in chinese if you located in China.

there is one way to change it into english

1.find sqldeveloper.conf in location ../sqldeveloper/bin/sqldeveloper.conf

2.open it,and add below 2 item 

AddVMoption -Duser.language=en

AddVMoption -Duser.country=US

3.save and run sql developer again,you will find the UI is all in english now.