sort by article number with polylang – customisation

Hallo, i have already an working sort by article number…now the point is, i want it multilingual with polylang, i tried several things, but it is not working. the working part is:

add_filter( 'woocommerce_get_catalog_ordering_args', 'custom_woocommerce_get_catalog_ordering_args' );

function custom_woocommerce_get_catalog_ordering_args( $args ) {
$orderby_value = isset( $_GET['orderby'] ) ? woocommerce_clean( $_GET['orderby'] ) : apply_filters( 'woocommerce_default_catalog_orderby', get_option( 'woocommerce_default_catalog_orderby' ) );

if ( 'random_list' == $orderby_value ) {
$args['orderby'] = 'meta_value';
$args['order'] = 'asc';      //asc 
$args['meta_key'] = '_sku';
}

return $args;
}

//Sorting names for Frontend and Backend
add_filter( 'woocommerce_default_catalog_orderby_options', 'custom_woocommerce_catalog_orderby' );
add_filter( 'woocommerce_catalog_orderby', 'custom_woocommerce_catalog_orderby' );

function custom_woocommerce_catalog_orderby( $sortby ) {
$sortby['random_list'] = 'Sort by Item number'; //Sorting by Item
return $sortby;
}

i tried:

if(pll_current_language() == 'en') {
                    function custom_woocommerce_catalog_orderby( $sortby ) {
$sortby['random_list'] = 'Sort by Item number';      //Name Sort by Item nr
return $sortby;
}
                } else if(pll_current_language() == 'de') {
                    function custom_woocommerce_catalog_orderby( $sortby ) {
$sortby['random_list'] = 'Artikelnummer aufsteigend';      //Name Sortierm?glichkeit
return $sortby;
} 
                }

and is not working.

how can i make a value also for german, italian…etc? like:

$sortby['random_list'] = 'Sortieren nach Artikennr'; //Sorting by Item DE-german etc.? Thanks

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