How to detect the local of the client (Browser)

Hello guys,
I trying to make my application international so I'm retreiving data from properties files in the Server (with Spring), but I want to locate the language of my browser's client in my EntryPoint how can I do it?
in my EntryPoint I retreive the locale Language, I send it to the Server with and RPC Call, and I receive the valid properties key/value in a HashMap. thats my scenario.
thanks