Language Change

Hi, I have tried to change the language of the plugin by changing the short code from [dopbs] to [dopbs lang=es], for Spanish, but it gives me an error:

“Warning: include_once(translation/frontend/es.php) [function.include-once]: failed to open stream: No such file or directory in /home/paseosma/public_html/wp-content/plugins/booking-system/dopbs-frontend.php on line 99

Warning: include_once() [function.include]: Failed opening ‘translation/frontend/es.php’ for inclusion (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/paseosma/public_html/wp-content/plugins/booking-system/dopbs-frontend.php on line 99″

How should I do to change language to Spanish?

Thanks

https://wordpress.org/plugins/booking-system/