Running MediaWiki 1.31.1 in PHP 7.3.0RC4 produces the following warnings:
PHP Warning: "continue" targeting switch is equivalent to "break". Did you mean to use "continue 2"? in /var/www/www.dxgl.org/w/includes/json/FormatJson.php on line 297 PHP Warning: "continue" targeting switch is equivalent to "break". Did you mean to use "continue 2"? in /var/www/www.dxgl.org/w/languages/LanguageConverter.php on line 773