It should!
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.
<rdar://problem/8494337>
Created attachment 71208 [details] proposed patch
Comment on attachment 71208 [details] proposed patch View in context: https://bugs.webkit.org/attachment.cgi?id=71208&action=review > WebCore/platform/mac/Language.mm:95 > + preferredLanguageCode = [@"en" retain]; No need to retain a constant string.
Committed <http://trac.webkit.org/changeset/70095>.