WooCommerce: Add custom tabs

functions.php

/**
 * Add custom tabs
 * Author: MarioMarkovic.com
 */
add_filter( 'woocommerce_product_tabs', 'custom_product_tabs' );
function custom_product_tabs( $tabs ) {
    if(get_field('navodila_za_uporabo')) {
        $tabs['general'] = array(
            'title' => __('Navodila za uporabo', 'nm-framework'),
            'callback' => 'product_tab_instructions_content',
            'priority' => 50,
        );
    }

    return $tabs;
}

/**
 * Function that displays output for the custom tab - General.
 * Author: MarioMarkovic.com
 */
function product_tab_instructions_content( $slug, $tab ) {
    // get_template_part( 'template-parts/tabs/instructions' );
    echo "Custom tab";
}