Add localized JavaScript variables to WordPress theme

functions.php

<?php
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );
function my_theme_enqueue_styles() {
	wp_localize_script(
		'script',
		'i18n',
		array(
			'download' => __( 'Download file', 'mytheme' ),
		)
	);
}