you can add the lang parameter to your loop arguments like so
$loop = new WP_Query( array (
'post_type' => 'post',
'lang' => pll_current_language('slug'), //returns 'en' for example
'posts_per_page' => 10,
'post_status' => 'publish',
) );
However this is not the better practice because by doing that way we override the main query which is not wp friendly.
We should better do like this using the pre_get_post action hook, so in your functions.php file:
if(function_exists('pll_current_language')) // if polylang
{
add_action( 'pre_get_posts', 'include_language' );
function include_language( $query )
{
if ( $query->is_main_query() ) { //add more condition here if needed
$query->set( 'lang', pll_current_language('slug') );
}
}
}