Get the link text

How I can get the link text is using WordPress?

By default is something like:

Read More <span class="meta-nav">→</span>

buy I want to get that value in a variable because some WordPress installation can have that value customized (using filter the_content_more_link) or in another language.

In resumen: what I need is to get from WordPress the text (the HTML code) that WordPress uses to replace the when display a Post Content.

You can use posts custom fields to store a custom continue reading text for each post, and then use that value in the_content_more_link filter. For example you might have a custom field with meta key of continue_reading to enable users to specify the custom Read More text, and use that value like:

add_filter('the_content_more_link', 'ad_contiue_reading_text',10,2);
function ad_contiue_reading_text($content_more_link, $read_more_text) {

    $post = get_post();
    $new_read_more_text = get_post_meta($post->ID, 'continue_reading', true);
    // .. or any text you want, for example:
    // $new_read_more_text="Discover More <span>&rarr;</span>";

    if($new_read_more_text) {
        $content_more_link = str_replace($read_more_text, $new_read_more_text, $content_more_link);
    }

    return $content_more_link;
}