jetpack_instant_search_options

snippet.php

add_filter( 'jetpack_instant_search_options', function($options) {
    $lang = pll_current_language();

    $options['adminQueryFilter'] = array(
        'bool' => array(
            'must' => array(
                array( 'term' => array( 'taxonomy.language.slug' => $lang ) ),
            )
        )
    );

    return $options;
} );