Appontments+ - setting the language

Hi there,

I'm trying to set the language for Appointments+ to Dutch. I have done the following:

1. Downloaded the necessary files and placed them in the plugins/appointmentsplus/languages:

2. Although deprecated but recommended in a post, I added define ('WPLANG', 'nl_NL'); to wp_config.php

Still the Appointments+ is in english. What am I missing here?

kind regards,