Quote Originally Posted by glenara View Post
The issue is two fold, you may multiple languages in your website but only one in the admin section to administer the site.

If you add a language and it does not exist in the admin section you should not get an error.
One serious caveat: if you're corresponding with customers from your admin, all correspondence will happen in the selected language. So, if you're sending emails from your admin while in "English", then all your emails will go to the customer in English, even if the customer did their shopping in French or Spanish, or whatever. If you want the emails to be sent from the other language, you need to switch to that language first. But, if you haven't installed that language on your admin side, then ... well ... you won't be able to do that.
It's your customers who suffer when you don't install the admin-side language pack.