According to Spotify Object Model, Episode objects contain a languages property that is a list of ISO 639 language codes. This is a lie. In reality they can contain country codes too, such as en-US or en-GB. However, there is no documentation or explanation of this anywhere in the Spotify Web API website.
On a similar but unrelated note, Spotify endpoints can return the country code XK in the available_markets parameter, which is not part of the ISO 3166 standard - it would be helpful to indicate that Spotify is using an extended version of the standard in the documentation.