Have done a temporary workaround of the Locale issue by globalling changing all instances of "class Locale ", "Locale::" and "Locale ::" to "class LocaleX" etc.
This got rid of the fatal Locale error. Then came a timezone warning, which I fixed by adding date_default_timezone_set('mycountry/mylocale') to index.php.
But I'm still getting a blank page, and there are no more error messages to help me along. I've got stacktrace turned on in config.inc.php, and have added ini_set('display_errors', E_ALL); to index.php. But nothing is displaying, not the tiniest little error message, and neither Apache's error_log nor access_log are throwing up errors.
There is one change; the address bar now says http://mydomain/ojs/index.php/index/install
By the way, this in a linux installation; had no problems at all installing on a Windows machine.