You have to add the ‘lang’ parameter to your query.
Then you can set it to an empty string in order to query posts from all languages, or to one or more language codes.
Examples:
// All languages
$the_query = new WP_Query( array( [...], 'lang' => '') );
// English only
$the_query = new WP_Query( array( [...], 'lang' => 'en') );
// English and French only
$the_query = new WP_Query( array( [...], 'lang' => 'en,fr') );
See this page