When you install woocommerce-nl on an English WordPress (or any other language except Dutch) the plugin will not translate woocommerce. Off course this is how it should work but it can be confusing for the user.
Maybe it is a good idea (and this should be handy to in the gravityforms-nl plugin) to check if WP_LANG is set to nl_NL when a user activates the plugin, if not display an error message.
Great plugin!!! Thanks Pronamic!