Hi mixali,
Are you using premium version of the theme? Because the linked (free) version does not seem to have any custom post types.
Anyway, I guess the theme does not define custom types it provides as public (makes quite sense for slider post type), so Polylang doesn’t pick them as translatable by default.
You can try to use pll_get_post_types filter to add such post types. Unfortunately, I don’t know the exact name of the post types provided by your theme, so you have to find it yourself: you can find it via URL in the browser address bar when you go to the admin page listing all your custom post types, it should look something like: wp-admin/edit.php?post_type=post_type_name. My guess is it will be slider or something similar.
Then try to add the following snippet to your theme functions.php file, but replace both occurences of post_type_name with the actual post type name:
function mixali_pll_get_post_types($post_types) {
$post_types['post_type_name'] = 'post_type_name';
return $post_types;
}
add_filter('pll_get_post_types', 'mixali_pll_get_post_types');
Be sure to not remove the apostrophes!
