file.js

(function(){
	console.log(ait_php_var);
})();

file.php

<?php // used as a plugin
add_action( 'wp_enqueue_scripts', function() {
	$ait_pfad        = plugin_dir_url( __FILE__ ) . '/assets/js/ait_buttons.js';
	$ait_add_options = 'here';

	// Enqueued script with localized data.
	wp_register_script( 'ait_js_script', $ait_pfad );

	// Localize the script with new data
	wp_localize_script( 'ait_js_script', 'ait_php_var', [
		'external_link'  => __( 'Ext. Link', 'add-infos-to-the-events-calendar' ),
		'category_event' => __( 'Event Category', 'add-infos-to-the-events-calendar' ),
		'internal_link'  => __( 'Int. Link', 'add-infos-to-the-events-calendar' ),
		'ackids'         => $ait_add_options,
	] );
	// Enqueue the script after localizing
	wp_enqueue_script( 'ait_js_script' );
}, 10 );