translation of this module

Well, i have tried to export .pot and .po language files. But obivously there is some text of the module that does not come with those files, but are inside the module files.

like
define('REFERRALSOURCE_FIELDSET_TITLE_DEFAULT', 'Where did you hear about us?');
define('REFERRALSOURCE_FIELDSET_DESCRIPTION_DEFAULT', 'We would love to know where you heard about us!');
define('REFERRALSOURCE_SELECT_LABEL_DEFAULT', 'Selection');
define('REFERRALSOURCE_OTHER_LABEL_DEFAULT', 'Other');
....
from the file referralsource.modulde

I have not done any translation work of a module before ... but wondering now why these text-parts don't get exported to .pot and .po files?