To many iterations of debugging messed up everything. I wrote correct initially, the index.php language file has the following, so when it is not included, the constant appears instead of the formatted greetings string.

To fix it, I moved it to the english.php of my template:

PHP Code:
define('TEXT_GREETING_GUEST''Welcome <span class="greetUser">Guest</span>');
define('TEXT_GREETING_PERSONAL''Welcome <span class="greetUser">%s</span>'); 
Its working now.

Regards