Find hardcoded strings in the MassAction extension code and add i18n to allow i18n; rewrite and document the messages as appropriate per https://www.mediawiki.org/wiki/I18n. So the whole idea is looking through all files of this extension and finding hard-coded strings then use i18n them so they can be easily localized. Below are a few;
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/MassActionSpecialPage.php#L501
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Actions/RegexReplaceAction.php#L89
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Actions/AppendAction.php#L40
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Actions/AppendAction.php#L40
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Actions/AppendAction.php#L37
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Actions/RegexRenameAction.php#L89
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Matchers/TitleRegexMatcher.php#L81
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Matchers/TitleRegexMatcher.php#L98
* https://github.com/wikimedia/mediawiki-extensions-MassAction/blob/master/src/Targets/WikiPage/Matchers/TitleRegexMatcher.php#L102