How to create some sort of word mapping?

You just need to set your words in a WordPress translation tag in your theme:

<?php _e('Goedemorgen','yourthemename');?>

And with the WPML string translation tool you can scan for these strings and give the appropriate translation. That’s how I do it with the paying WPML plugin. Works like a breeze.

No need to make your own pot translation files (that’s maybe the answer you were initially looking for, but the WPML plugin makes things easier)