Adds polylang_translations and keeps lang to WP REST api response for each Post and Page request for site running the Polylang Pro plugin.
The locale value of the post
{
[...]
"lang": "en"
[...]
}
List of translation for the post
{
[...]
"polylang_translations": [
{
"lang": "fr",
"id": 1
}
],
[...]
}