Dear Maintainer,

This is what the browser shows instead of the Wiki start page:

MediaWiki internal error.

Original exception: [9d4e04feb2ee66c6ca3c10ff] /mediawiki/ UnexpectedValueException: Error: invalid magic word 'formal'
Backtrace:
from /usr/share/mediawiki/includes/parser/MagicWord.php(105)
#0 /usr/share/mediawiki/includes/parser/MagicWordFactory.php(177): MediaWiki\Parser\MagicWord->load()
#1 /usr/share/mediawiki/includes/parser/Parser.php(5057): MediaWiki\Parser\MagicWordFactory->get()
#2 /usr/share/mediawiki/includes/parser/CoreParserFunctions.php(129): MediaWiki\Parser\Parser->setFunctionHook()
#3 /usr/share/mediawiki/includes/parser/Parser.php(534): MediaWiki\Parser\CoreParserFunctions::register()
#4 /usr/share/mediawiki/includes/parser/ParserFactory.php(213): MediaWiki\Parser\Parser->__construct()
#5 /usr/share/mediawiki/includes/language/MessageCache.php(1488): MediaWiki\Parser\ParserFactory->create()
#6 /usr/share/mediawiki/includes/language/MessageCache.php(1469): MessageCache->getParser()
#7 /usr/share/mediawiki/includes/Message/Message.php(1533): MessageCache->transform()
#8 /usr/share/mediawiki/includes/Message/Message.php(1078): MediaWiki\Message\Message->transformText()
#9 /usr/share/mediawiki/includes/Message/Message.php(1127): MediaWiki\Message\Message->format()
#10 /usr/share/mediawiki/includes/user/UserGroupMembership.php(254): MediaWiki\Message\Message->text()
#11 /usr/share/mediawiki/includes/user/UserGroupMembership.php(225): MediaWiki\User\UserGroupMembership::getGroupPage()
#12 /usr/share/mediawiki/includes/user/UserGroupMembership.php(182): MediaWiki\User\UserGroupMembership::getLinkInfo()
#13 /usr/share/mediawiki/includes/Permissions/PermissionManager.php(729): MediaWiki\User\UserGroupMembership::getLinkWiki()
#14 /usr/share/mediawiki/includes/Permissions/PermissionManager.php(708): MediaWiki\Permissions\PermissionManager->newFatalPermissionDeniedStatus()
#15 /usr/share/mediawiki/includes/Permissions/PermissionManager.php(686): MediaWiki\Permissions\PermissionManager->missingPermissionError()
#16 /usr/share/mediawiki/includes/Permissions/PermissionManager.php(507): MediaWiki\Permissions\PermissionManager->checkReadPermissions()
#17 /usr/share/mediawiki/includes/Permissions/UserAuthority.php(372): MediaWiki\Permissions\PermissionManager->getPermissionStatus()
#18 /usr/share/mediawiki/includes/Permissions/UserAuthority.php(232): MediaWiki\Permissions\UserAuthority->internalCan()
#19 /usr/share/mediawiki/includes/user/User.php(3318): MediaWiki\Permissions\UserAuthority->authorizeRead()
#20 /usr/share/mediawiki/includes/actions/ActionEntryPoint.php(405): MediaWiki\User\User->authorizeRead()
#21 /usr/share/mediawiki/includes/actions/ActionEntryPoint.php(146): MediaWiki\Actions\ActionEntryPoint->performRequest()
#22 /usr/share/mediawiki/includes/MediaWikiEntryPoint.php(200): MediaWiki\Actions\ActionEntryPoint->execute()
#23 /usr/share/mediawiki/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#24 {main}

Exception caught inside exception handler: [9d4e04feb2ee66c6ca3c10ff] /mediawiki/ UnexpectedValueException: Error: invalid magic word 'formal'
Backtrace:
from /usr/share/mediawiki/includes/parser/MagicWord.php(105)
#0 /usr/share/mediawiki/includes/parser/MagicWordFactory.php(177): MediaWiki\Parser\MagicWord->load()
#1 /usr/share/mediawiki/includes/parser/Parser.php(5057): MediaWiki\Parser\MagicWordFactory->get()
#2 /usr/share/mediawiki/includes/parser/CoreParserFunctions.php(129): MediaWiki\Parser\Parser->setFunctionHook()
#3 /usr/share/mediawiki/includes/parser/Parser.php(534): MediaWiki\Parser\CoreParserFunctions::register()
#4 /usr/share/mediawiki/includes/parser/ParserFactory.php(213): MediaWiki\Parser\Parser->__construct()
#5 /usr/share/mediawiki/includes/language/MessageCache.php(1488): MediaWiki\Parser\ParserFactory->create()
#6 /usr/share/mediawiki/includes/language/MessageCache.php(1469): MessageCache->getParser()
#7 /usr/share/mediawiki/includes/Message/Message.php(1533): MessageCache->transform()
#8 /usr/share/mediawiki/includes/Message/Message.php(1078): MediaWiki\Message\Message->transformText()
#9 /usr/share/mediawiki/includes/Message/Message.php(1127): MediaWiki\Message\Message->format()
#10 /usr/share/mediawiki/includes/Output/OutputPage.php(1149): MediaWiki\Message\Message->text()
#11 /usr/share/mediawiki/includes/Output/OutputPage.php(1225): MediaWiki\Output\OutputPage->setHTMLTitle()
#12 /usr/share/mediawiki/includes/Output/OutputPage.php(1213): MediaWiki\Output\OutputPage->setPageTitleInternal()
#13 /usr/share/mediawiki/includes/exception/MWExceptionRenderer.php(181): MediaWiki\Output\OutputPage->setPageTitleMsg()
#14 /usr/share/mediawiki/includes/exception/MWExceptionRenderer.php(109): MWExceptionRenderer::reportHTML()
#15 /usr/share/mediawiki/includes/exception/MWExceptionHandler.php(135): MWExceptionRenderer::output()
#16 /usr/share/mediawiki/includes/exception/MWExceptionHandler.php(239): MWExceptionHandler::report()
#17 /usr/share/mediawiki/includes/MediaWikiEntryPoint.php(222): MWExceptionHandler::handleException()
#18 /usr/share/mediawiki/includes/actions/ActionEntryPoint.php(82): MediaWiki\MediaWikiEntryPoint->handleTopLevelError()
#19 /usr/share/mediawiki/includes/MediaWikiEntryPoint.php(206): MediaWiki\Actions\ActionEntryPoint->handleTopLevelError()
#20 /usr/share/mediawiki/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#21 {main}

Dear Maintainer,

the following steps provided a partial solution:

- change Media Wiki's database password so the database could not be wiped
- purge the Media Wiki packages
- apt autoremove
- install Media Wiki
- restore /etc/mediawiki and /var/lib/mediawiki from my regular backups
- images did not show → edited one link, problem resolved

I hit the same problem.

The suggested workaround sounded a bit long winded so I deleted
/etc/mediawiki/LocalSettings.php then went to
http://my-server/mediawiki/mw-config to generate a new one.

Installing the new LocalSettings.php  was enough for it to spring back
into life.

I then restored my old LocalSettings.php and verified it was back to
broken state.

Next I added the line

$wgLanguageCode = "en-gb";

to LocalSettings.php and it was back up and running.

Finally I switched back to the new LocalSettings.php because my old one
was so old (2012 I think) that I figured it would cause more pain in the
future.