How translate the template amp-index.php?

I installed the plugin from GitHub repository

I’m working on a custom template using the filter amp_template_file, works fine. Like this:

add_filter('amp_template_file', 'proceso_amp_template_file');
function proceso_amp_template_file($default_template){
	return locate_template('amp/templates/amp-index.php');
}

In the original template file amp-index.php I see the line number 212 and I want to apply the translation.

<?php echo esc_html( sprintf( _x( 'Posted %s ago', '%s = human-readable time difference', 'amp' ), human_time_diff( get_the_date( 'U', $post_id ) ) ) ); ?>

Create the file es_MX.po and compiler to create the file es_MX.mo .

I used the functions load_plugin_textdomain , load_theme_textdomain , load_textdomain and I failed to apply the translation.

I come to you for help on how I can apply the translation.

Thanks.

https://wordpress.org/plugins/amp/