If a “Registration required to apply updates” message appears when you are attempting to patch your older version of The Witcher with the Enhanced Edition patch you don’t have to actually register. It is not necessary, nor possible to register the game through the Launcher (the option is obsolete now, the Launcher was created many years ago.)
If an old version of The Witcher requests registration to apply updates it means you have an old (pre-August 2011) version of the Enhanced Edition patch. Download the current version of the Enhanced Edition patch and the language packs, which have to be applied with it.
An alternative solution to patching the older versions of The Witcher is to claim the digital backup copy of the game on gog.com/witcherbackup (more info available here). The gog.com version of The Witcher is fully updated from the very moment it is installed and doesn’t need to be patched.