How to change default char set?

Been trying to install AjaXplorer but get two errors on running the test.

One being:

You must set a correct charset encoding in your locale definition in the form: en_us.UTF-8. Please refer to setlocale man page. If your detected locale is C, please check the F.A.Q.. Detected locale: C (using UTF-8)

I checked their FAQ but it wasn't much help.

If I try and run it anyway I get the following:

Exception thrown within the exception handler! Message was: Cannot find plugin text for type log in C:\UniServer\www\domain\secure\core\classes\class.ConfService.php on line 164 #0 C:\UniServer\www\domain\secure\core\classes\class.ConfService.php(184): ConfService->initUniquePluginImplInst('LOG_DRIVER', 'log') #1 C:\UniServer\www\domain\secure\core\classes\class.ConfService.php(229): ConfService->getUniquePluginImplInst('LOG_DRIVER', 'log') #2 C:\UniServer\www\domain\secure\core\classes\class.AJXP_Logger.php(89): ConfService::getLogDriverImpl() #3 C:\UniServer\www\domain\secure\core\classes\class.AJXP_Logger.php(69): AJXP_Logger::getInstance() #4 C:\UniServer\www\domain\secure\core\classes\class.AJXP_XMLWriter.php(195): AJXP_Logger::logAction('error', Array) #5 C:\UniServer\www\domain\secure\core\classes\class.AJXP_XMLWriter.php(208): AJXP_XMLWriter::catchError(0, 'Cannot find plu...', 'C:\UniServer\ww...', 164, NULL) #6 [internal function]: AJXP_XMLWriter::catchException(Object(Exception)) #7 {main}

Not sure if it would be because of the errors I was given in the test