How do I define a lookup table that will work across all PHP elements of the template?

Question

Loading it in the header should work, or on the init hook. You will need to declare it global as well. So…

// define
global $trans_home;
$trans_home = array('en' => 'Home','it' => 'Home','de' => 'Home','zh' => '首页','es' => 'Página de inicio','fr' => 'Page d\'accueil');

// and use in your templates
global $trans_home;
echo $trans_home[qtrans_getLanguage()];