We should make CreateWiki's default i18n, for example, createwiki-defaultmainpage, non-Miraheze-specfic. Since we try to avoid Miraheze-specific code in our extensions, we should make the current default i18n that is Miraheze-specific as overrides in MirahezeMagic.
I know there is a lot of other Miraheze-specific code in CreateWiki, but this is also a good start for removing it.