Mac is somewhat special in that there is a way to override language per application (or even per an instance of an application). This means that we should only be looking at the language in UI process.
Created attachment 71208 [details]
Comment on attachment 71208 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=71208&action=review
> + preferredLanguageCode = [@"en" retain];
No need to retain a constant string.