I'm trying to get my Silverlight Client localized, but I'm stuck with the Add/Edit dialog boxes being localized as well. Everything works correctly except these dialogs. Here are some screenshots:
Here's the localization settings:

It's working fine on the grid:

But not on the Add/Edit dialogs:

You need to localize the server tier.
To do so :
Take a look at: Walkthrough: Localizing a LightSwitch Application (jump to: To localize the server tier) http://msdn.microsoft.com/en-us/library/Xx130603(v=VS.120,d=hv.2).aspx