This is what worked for me (based on this).. hope it will be helpful for others too..
add_filter( 'wp_nav_menu_items','primary_navigation', 10, 2 );
function primary_navigation( $items, $args ) {
if( $args->theme_location == 'primary_navigation' ) {
if ( ! isset( $_SESSION['menu_country'] ) ) {
$country = json_decode( file_get_contents(
"http://freegeoip.net/json/" . esc_url( $_SERVER['REMOTE_ADDR'] )
) );
$_SESSION['menu_country'] = strtolower( $country->country_code );
}
$items .= '<li class="menu-produkte"><a href="https://wordpress.stackexchange.com/" .
esc_url( $_SESSION['menu_country'] ) .'/shop">Produkte</a></li>';
}
return $items;
}