I'm running a media wiki on Archlinux and php version update often, current version: php 7.0.2
In the log, I can see that is due to a php Fatal error on Translate extension:
2016-01-11 17:02:31: (mod_fastcgi.c.2520) FastCGI-stderr: PHP message: PHP Fatal error: Redefinition of parameter $_ in /usr/share/webapps/mediawiki/extensions/Translate/tag/PageTranslationHooks.php on line 103
Thanks for your help, my wiki is in multi-lang so disabling this extension is not an option.