Wi-fi or Internet?  In order to use wi-fi you need to be around a wireless connection that your phone knows the user name/password to (or is an open connection that you have chosen to trust).

If you mean Internet, then it might be your translator program. If it is Google, then it will often not work because Google runs really randomly in China due to the wonderful folks in the Chinese censor department.

There are phone translators out there that pull results from multiple search engines like Bing, Google & others for comparison, but they also work well when one of them is having issues so that you can at least get something translated.