Make sure that you're putting the locale keys of your translation into the same files that their English equivalents appear in -- for example,
admin.scheduledTask.clearLogs appears in
lib/pkp/locale/en_US/admin.xml, so make sure you put it in the same place. If it's there, and you still don't see the translation appearing, try validating the XML with a good XML editor or a tool like
xmllint to ensure that you haven't accidentally entered a typo that prevents the file from parsing.
Public Knowledge Project Team