Seen 17 times in the last few hours. Started in wmf.13.
Can be reproduced in two ways:
* API: Request parser information about a pre-existing page already containing `#babel:simple`, e.g. <https://meta.wikimedia.org/w/api.php?action=parse&title=User%3AQuiddity+%28WMF%29&text=%7B%7B%3AUser%3AQuiddity+%28WMF%29%7D%7D&uselang=en&format=json>.
* Web: Preview or save a page containing `#babel:simple`, e.g. <https://meta.wikimedia.org/w/index.php?title=User:Quiddity_(WMF)&action=edit> => "Show preview"
```counterexample
type: mediawiki
channel: exception
exception.class: MWException
Language::isValidBuiltInCode must be passed a string, boolean given
```
```lines=10
#0 /srv/mediawiki/php-1.32.0-wmf.13/languages/Language.php(213): Language::isValidBuiltInCode(boolean)
#1 /srv/mediawiki/php-1.32.0-wmf.13/languages/Language.php(191): Language::newFromCode(boolean)
#2 /srv/mediawiki/php-1.32.0-wmf.13/extensions/Babel/includes/BabelBox/LanguageBabelBox.php(85): Language::factory(boolean)
#3 /srv/mediawiki/php-1.32.0-wmf.13/extensions/Babel/includes/Babel.php(190): MediaWiki\Babel\BabelBox\LanguageBabelBox->render()
#4 /srv/mediawiki/php-1.32.0-wmf.13/extensions/Babel/includes/Babel.php(109): Babel::mGenerateContent(Parser, string, array)
#5 /srv/mediawiki/php-1.32.0-wmf.13/extensions/Babel/includes/Babel.php(47): Babel::mGenerateContentTower(Parser, array)
#6 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Parser.php(3434): Babel::Render(Parser, string, string, string, string, string)
#7 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Parser.php(3138): Parser->callParserFunction(PPTemplateFrame_Hash, string, array)
#8 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Preprocessor_Hash.php(1114): Parser->braceSubstitution(array, PPTemplateFrame_Hash)
#9 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Preprocessor_Hash.php(1546): PPFrame_Hash->expand(PPNode_Hash_Tree, integer)
#10 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Parser.php(3310): PPTemplateFrame_Hash->cachedExpand(string, PPNode_Hash_Tree)
#11 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Preprocessor_Hash.php(1114): Parser->braceSubstitution(array, PPFrame_Hash)
#12 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Parser.php(2953): PPFrame_Hash->expand(PPNode_Hash_Tree, integer)
#13 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Parser.php(1297): Parser->replaceVariables(string)
#14 /srv/mediawiki/php-1.32.0-wmf.13/includes/parser/Parser.php(446): Parser->internalParse(string)
#15 /srv/mediawiki/php-1.32.0-wmf.13/includes/StubObject.php(112): Parser->parse(string, Title, ParserOptions, boolean, boolean, NULL)
#16 /srv/mediawiki/php-1.32.0-wmf.13/includes/StubObject.php(138): StubObject->_call(string, array)
#17 /srv/mediawiki/php-1.32.0-wmf.13/includes/content/WikitextContent.php(323): StubObject->__call(string, array)
#18 /srv/mediawiki/php-1.32.0-wmf.13/includes/content/AbstractContent.php(516): WikitextContent->fillParserOutput(Title, NULL, ParserOptions, boolean, ParserOutput)
#19 /srv/mediawiki/php-1.32.0-wmf.13/includes/api/ApiParse.php(268): AbstractContent->getParserOutput(Title, NULL, ParserOptions)
#20 /srv/mediawiki/php-1.32.0-wmf.13/includes/api/ApiMain.php(1584): ApiParse->execute()
#21 /srv/mediawiki/php-1.32.0-wmf.13/includes/api/ApiMain.php(535): ApiMain->executeAction()
#22 /srv/mediawiki/php-1.32.0-wmf.13/includes/api/ApiMain.php(506): ApiMain->executeActionWithErrorHandling()
#23 /srv/mediawiki/php-1.32.0-wmf.13/api.php(83): ApiMain->execute()
#24 /srv/mediawiki/w/api.php(3): include(string)
#25 {main}
```