Facebook's Open Graph Protocol markup allows for defining the current web page's locale, and any alternative locales it's also available in, using a markup like this:
<meta property="og:locale" content="en_GB">
<meta property="og:locale:alternate" content="fr_FR">
<meta property="og:locale:alternate" content="es_ES">
The current page's permalink can be easily deduced (from the URL, Canonical URL meta tag, or og:url).
But what's the point of including og:locale:alternate without their respective URLs? How is it at all useful?