I need to change the text of “In stock” and “Out of stock” variable products.
I used this code:

// change stock text
add_filter( 'woocommerce_get_availability', 'wcs_custom_get_availability', 1, 2);

function wcs_custom_get_availability( $availability, $variation ) {

    // Change In Stock Text
    if (  $variation->is_in_stock() ) {
        $availability['availability'] = __('Available!', 'woocommerce');
    }
    // Change Out of Stock Text
    if ( ! $variation->is_in_stock() ) {
        echo '-------------------------';
        echo __('Sold Out', 'woocommerce');
        $availability['availability'] = __('Sold Out', 'woocommerce');
    }

    return $availability;

}

It works fine for the available product, but not for the out-of-stock one.