I am using a WiX installer to deploy my .Net application. I have a custom action to run my application executable with a special parameter in order to copy some localized files to the Public Documents folder.
<CustomAction Id='Foo' ExeCommand='-special-parameter' FileKey='application' Impersonate='no' Execute='deferred'/>
On my testing machine, I have Windows 7 Ultimate (x86 installed from an English CD) with several additional languages installed and I am running as a user with admin privileges. I have set the display language in the Control Panel to French and restarted, as I am directed according to this link

In my application, during the custom action mentioned above, CultureInfo.CurrentUICulture returns English. But when I run my application after install, CultureInfo.CurrentUICulture returns French as expected.
Why is Windows returning the wrong culture during the install process? Is it because the installer does not run as the logged in user? Or is this related to the fact that Windows was installed using an English CD?
Based on the steps outlined, you have not changed the language used by system reserved accounts (likely English since you installed from an English language CD). Click the ‘Administration’ tab (visible in your picture), then click the ‘Copy Settings’ button. From there you can makes changes for system accounts. Try that and run your installer again.
Follow up: I note that your custom action is set to not impersonate. If it did, you would likely see the correct language as well. The downside would be that it might not be able to accomplish what it is meant to do.
Source : http://www.mydigitallife.info/change-display-language-for-windows-7-ui-welcome-screen-system-and-new-accounts/