ah, so you want to change the texts that are visible on the frontend (where site visitors see the table) to English as well, and not just the admin area of WP-Table Reloaded?
Unfortunately, that is not this easy, as the setting in the "Plugin Options" only changes the language in the admin area.
To be able to change the language for the frontend, I suggest that you already switch to the official and designated successor of WP-Table Reloaded, namely TablePress, which you can find at http://wordpress.org/extend/plugins/tablepress/description/
TablePress also allows you to change the language for the admin area (actually it doesn't yet support Dutch, so it will be in English right now anyway), but it also allows you to change the language on the frontend with the help of a new parameter for the Shortcode. In TablePress, you just need to embed the table with the Shortcode
[table id=123 datatables_locale="en_US" /]
to get it in English, regardless of what the language of the admin area is.