[minorgod]

Okay, so now I've discovered that the problem wasn't realated to the above errors. It turns out that for some reason the default store language was not being selected for users who had not already received a cookie to set their default language. I discovered this after I deleted all my browser cookies and then was finally able to reproduce the problem in my store. After running the pages in my remote debugger (PHPed rocks for this) I discovered that the /include/get_language.php file was the culprit. The problems seem to start on line 15 where it says

$customer_language = func_get_language ($store_language);
		if (!$customer_language]) {
			$store_language = $config["default_customer_language"];
			$customer_language = func_get_language ($store_language);
		}

It seems that the $customer language variable was returning a 1 element array with an empty key name and an empty string as the value. So in the next line it was skipping the default language assignment. I don't know why this just started happening, but I fixed it by changing the code to

$customer_language = func_get_language ($store_language);
		if (!$customer_language || empty($customer_language[0])) {
			$store_language = $config["default_customer_language"];
			$customer_language = func_get_language ($store_language);
		}

It's a dirty hack, but since I can't figure out why it broke in the first place I have no alternative but to use this hack.