I had an error in the qa-lang-emails.php (missing comma).
This causes the following line in qa_lang_base to fail silently, causing in turn a White Screen of Death:
$phrases=@include $directory.'qa-lang-'.$group.'.php'; // can tolerate missing file or directory
The fact that the translation file was corrupted is of course my bug, but would it be possible to fail in a more informative way?
I realize that it might mean you can't simply use php parser to include the language files (e.g. here http://stackoverflow.com/questions/1527364/php-robust-include-to-handle-errors
Maybe another format for the language files will anyway be better?