Exactly. Since XMLs are loaded into the cart's SQL only once (at the initial cart setup), in order for someone to change the spelling she would have to work with the System > Language Definitions filtering out a block name as "mail" , possibly to get lost in 3 pages of keys and translations. To select the right key, non-coders have to sign up as a test customer and trace back the key by the text in an email notification received in the Inbox.
While doable, there are situations when right block/key pair is too hard to guess from its name without checking the code. On the one hand, editing Definitions is cool and straightforward when you get used to it. On the other, we don't know if this is correct approach to rely on the Definitions that much in the cart.
We understand it's difficult to implement things like this --
http://forum.abantecart.com/index.php/topic,1253.0.html : simple WYSIWYG editor will not work because notifications are made of placeholders, not just a free text; and to combine both, you'd need something like the Design layout screen Lee mentioned. Or users would need to learn every placeholder and put it into the editor text themselves... Would it become a placeholder nightmare prone to errors and make the cart overly complex? Just thinking how to facilitate managing that for new AC admins without making it worse. Maybe an easy way to find the right block/key pair for a non-coder would be OK, like a documented layout of each notification where each block/key pair is shown near default text, formatted as image or PDF doc linked from the admin panel ? It could be just part of the ecommerce-documentation, if there was way to make sure that new AC user would know it's there (currently there's no definite screen to link the help icon to, for the notifications).
Wish we could remove that Logo image from all e-mailed notifications, anyway..