I18n translation for Permissions is performed in VM template associated to WorkflowPermissionCondition, WorkflowPermissionValidation are based i18n ressources defined in ModuleDescriptor definition.
Extension of the i18n resource requires to modify system-workflow-plugin.xml by adding in each workflow module definition a new resource :

        <resource type="i18n" name="i18n" location="com.atlassian.jira.web.action.admin.permission.SchemeAwarePermissionAction"/>