How to change taxonomy slug?

Question

I have some registered taxonomies like this one:

/********************************* Género *****************************/

function genre_init() {
    $labels_genre = array(
    'name' => _x( 'Géneros', 'taxonomy general name' ),
    'singular_name' => _x( 'Género', 'taxonomy singular name' ),
    'search_items' =>  __( 'Buscar Género' ),
    'popular_items' => __( 'Géneros Populares' ),
    'all_items' => __( 'Todos los Géneros' ),
    'edit_item' => __( 'Editar Género' ),
    'update_item' => __( 'Update Género' ),
    'add_new_item' => __( 'Añadir nuevo Género' ),
    'new_item_name' => __( 'Nuevo nombre de Género' ),
    'separate_items_with_commas' => __( 'Separa Géneros con comas' ),
    'add_or_remove_items' => __( 'Añade o quita Géneros' ),
    'choose_from_most_used' => __( 'Elige entre los Géneros más utilizados' )
    );

    // create a new taxonomy
    register_taxonomy(
    'Géneros',
        'reviews',
        array(
            'rewrite' => array( 'slug' => 'genre' ),
            'labels' => $labels_genre
        )
    );
}
add_action( 'init', 'genre_init' );

/**********************************************************************/

When using a plugin to show the links of each taxonomy value (e.g. "rock", "folk", ...) I saw the accent in the slug (http://dcodedmagazine/?taxonomy=Géneros&term=rock), so I tried to change the taxonomy name:

/**********************************************************************/

/********************************* Género *****************************/

function genre_init() {
    $labels_genre = array(
    'name' => _x( 'Generos', 'taxonomy general name' ),
    'singular_name' => _x( 'Genero', 'taxonomy singular name' ),
    'search_items' =>  __( 'Buscar Género' ),
    'popular_items' => __( 'Géneros Populares' ),
    'all_items' => __( 'Todos los Géneros' ),
    'edit_item' => __( 'Editar Género' ),
    'update_item' => __( 'Update Género' ),
    'add_new_item' => __( 'Añadir nuevo Género' ),
    'new_item_name' => __( 'Nuevo nombre de Género' ),
    'separate_items_with_commas' => __( 'Separa Géneros con comas' ),
    'add_or_remove_items' => __( 'Añade o quita Géneros' ),
    'choose_from_most_used' => __( 'Elige entre los Géneros más utilizados' )
    );

    // create a new taxonomy
    register_taxonomy(
    'Generos',
        'reviews',
        array(
            'rewrite' => array( 'slug' => 'genre' ),
            'labels' => $labels_genre
        )
    );
}
add_action( 'init', 'genre_init' );

/**********************************************************************/

and now the in the plugin widget I have to choose "Genero" instead of "Géneros", but I'm still getting the same slug. I don't really understand why I'm not able to change the slug of a custom taxonomy created by me. Any idea of what I'm missing?

Edit:

Indeed, the other taxonomy slugs are: artistas=alice-in-chains and not: taxonomy=artistas&term=alice-in-chains.

2º Edit:

Debug mode was disabled. Enabling it I can see the next Notice for each "Géneros" field printed: Notice: Trying to get property of non-object in /home/user/MyServer/project/wp-includes/taxonomy.php on line 3185

Answer 1

It was a really silly issue. The same slug was used by a tag, so here was the problem. When I deleted the tag the problem disappeared.