suhosin.get.max_value_length??

[Apple]

Where do I find the following file/lines to change the max value "MediaWiki's ResourceLoader component will work around this limit, but that will degrade performance. If at all possible, you should set suhosin.get.max_value_length to 1024 or higher in php.ini, and set $wgResourceLoaderMaxQueryLength to the same value in LocalSettings.php."

[Skizzerz]

php.ini is a system configuration file. If you host your own server, you can find the ini file location in phpinfo(). If you have hosting elsewhere, contact your host and ask them to change the value in php.ini. Once changed in php.ini, you should modify your LocalSettings.php file as indicated.

As a side note, this is only relevant if you are still stuck on PHP 5. The most recent version of MediaWiki does not support PHP 5. If you are using PHP 7, the warning is meaningless and you can safely ignore it.