Update Pagefile::hasTag() and Pagefiles::getTag() and Pagefiles::findTag() to support OR tags, separated by "|", like "this-tag|that-tag".
Add a hook in LanguageSupportPageNames to Page::viewable. Now you can call $page->viewable($language) or $page->viewable('language-name') to see if the page is viewable by the current user in that language. Viewable in this case means that the page has its "active" box checked on the settings tab.