Source

File: wp-includes/class.wp-scripts.php

public function print_translations( $handle, $echo = true ) {
		if ( ! isset( $this->registered[ $handle ] ) || empty( $this->registered[ $handle ]->textdomain ) ) {
			return false;
		}

		$domain = $this->registered[ $handle ]->textdomain;
		$path   = $this->registered[ $handle ]->translations_path;

		$json_translations = load_script_textdomain( $handle, $domain, $path );

		if ( ! $json_translations ) {
			// Register empty locale data object to ensure the domain still exists.
			$json_translations = '{ "locale_data": { "messages": { "": {} } } }';
		}

		$output = <<<JS
( function( domain, translations ) {
	var localeData = translations.locale_data[ domain ] || translations.locale_data.messages;
	localeData[""].domain = domain;
	wp.i18n.setLocaleData( localeData, domain );
} )( "{$domain}", {$json_translations} );
JS;

		if ( $echo ) {
			printf( "<script%s id='%s-js-translations'>\n%s\n</script>\n", $this->type_attr, esc_attr( $handle ), $output );
		}

		return $output;
	}