With wikis with possibility of translation (with Extension:Translate), as MediaWiki, and to facilitate the translation of articles, these wikis use "constants" or pointers. For example:
...contribution under the [$cc0 CC0]. See [[$pd-help|Public Domain Help Pages]] for more info.
is compiled to:
...contribution under the [https://creativecommons.org/publicdomain/zero/1.0/ CC0]. See {{mediawiki|Project:PD help|Public Domain Help Pages}} for more info.
How to create these constants or variables or pointers (here $cc0 and $pd-help)?