Unfortunately, there is no information related to the language used by the NetSurveillance, but there is a way to find out how to change the language. Use a desktop PC/Mac, etc. and browse to the same website and then log-in with your username. Search the website the exact location from where you can change the language and then do the same on the iPhone 6. It should work this way. Of course, there is a possibility that Chinese to be the only language available for the system.
