Merge pull request #14981 from Volker-E/master

core/templates/403.php

core/templates/404.php

core/templates/error.php

core/templates/installation.php

core/templates/layout.base.php

core/templates/layout.guest.php

core/templates/layout.user.php

core/templates/login.php

core/templates/singleuser.user.php

core/templates/tags.html

core/templates/untrustedDomain.php

core/templates/update.user.php