Adding WPLANG to System Status

It takes an extra step when customers don't tell WooThemes what language they're using and the WPLANG constant also affects RTL support. It should be included when customers submit their system status for a more complete picture of what's going on.

It should look like this:
![woocommerce_status__test__wordpress](https://f.cloud.github.com/assets/1065372/927744/077d10d6-ffa6-11e2-8ea9-a200f523986b.png)


Inspired by: https://woothemes.zendesk.com/agent/#/tickets/84875