Within a skin

Use \Bootstrap\BootstrapManager::getInstance() to get the singleton managing the Bootstrap framework.

With the returned object,

• add Bootstrap modules using addBootstrapModule(), addCoreBootstrapModules(), and addAllBootstrapModules()
• set SCSS variables using setScssVariable() and setScssVariables()
• add style files using addStyleFile()
• add cache trigger files using addCacheTriggerFile()

Finally to add the Bootstrap styles and javascript to the page use $out->addModuleStyles( 'ext.bootstrap.styles' ) for styles and $out->addModules( 'ext.bootstrap.scripts' ) for scripts.

For an example on how to include Bootstrap styles in a skin have a look at the Chameleon skin.

Standalone

To simply enable Bootstrap styles on all pages add the following code to your "LocalSettings.php" file:

$wgHooks['SetupAfterCache'][] = function(){
	\Bootstrap\BootstrapManager::getInstance()->addAllBootstrapModules();
	return true;
};


$wgHooks['ParserAfterParse'][]=function( Parser &$parser, &$text, StripState &$stripState ){
	$parser->getOutput()->addModuleStyles( ['ext.bootstrap.styles'] );
	$parser->getOutput()->addModules( ['ext.bootstrap.scripts'] );
	return true;
};

Effect on Universal Language Selector

If you have the Universal Language Selector (ULS) extension installed, installing the Bootstrap extension will make the ULS's dropdown-menu look disordered and break its search bar (screenshot on GitHub). However, this can be fixed by adding the following code to MediaWiki:Common.css:

.uls-language-list {
        display: block;
}

.uls-search {
        display: block;
}