Is it valid to set the meta property="og:locale" to a two-letter value?

Question

We use 2-letter locales in our webpages (we don't differentiate between English or French flavors). I couldn't confirm in the documentation of OpenGraph if it is allowed:

<meta property="og:locale" content="en">

… or:

<meta property="og:locale" content="fr">

Is it valid? How to confirm if these values are taken into account?