Convert to modern functions all the (wfMsgGetKey|wfEmptyMsg|wfMsgReal) function usages listed in the description of https://phabricator.wikimedia.org/T70750 (extensions CommentPages, ConfirmAccount, GlobalNotice, ThemeDesigner, Transliterator).

Keep https://www.mediawiki.org/wiki/Localisation#Internationalization_hints in mind, study the messages API manual at https://www.mediawiki.org/wiki/Manual:Messages_API for PHP until you fully understand the conversion table: https://www.mediawiki.org/wiki/Manual:Messages_API#Help_with_replacing_deprecated_wfMsg.2A_functions