The error reporting uses json_encode flags which were introduced in 5.4.0. There needs to be some compatibility with older PHP versions as well.
Workarounded in https://github.com/phpmyadmin/phpmyadmin/commit/21812d6 . Though I have no clue whether removing JSON_UNESCAPED_SLASHES won't cause any troubles...
The json encode is a way to show the report to the user in a human readable format since print_r/var_dump is ugly. I am trying another method of displaying the report which we may use when we cant use the prettify json encode option.
any progress on your other method? I guess this is https://github.com/phpmyadmin/phpmyadmin/pull/735 and there are comments there to address.
I pushed some updates to the pull request, once they are merged they should be fixed I believe
Michal, please confirm.