Turning English off (using a custom English) in i18n breaks redirect on login

So WSF has a customization of the Drupal English, which we gave the prefix code "eng." This doesn't look as lovely as "en" but it works fine except for one place: when logging in and using redirection, you don't get to where you're headed. It somehow defaults to 'en' and directs you to a page with an en prefix, and because that's disabled, you get page not found.

This might be the cause, in i18n.module:

        // Worst case scenario: locale module not loaded, for cached pages, at least this won't break everything
        unset($languages); // There's some PHP bug: http://www.zend.com/zend/week/week98.php
        $languages['name'] = array('en' => 'English');

Changing line 399:

        $languages['name'] = array('eng' => 'English');

Seemed to fix things. Dirty hack, but it'll do for our specific site. If anyone else is using a customized English, or just has English disabled, this could help you too, until a proper fix gets into Internationalization (i18n) module or, possibly, Login Toboggan.

Resolution