Right align header's custom menu, when in RTL mode
theme/serenity/style/menu.css
theme/serenity/style/menu_rtl.css
theme/serenity/config.php
theme/serenity/renderers.php
theme/serenity/pix/menu/*

Support for blocks columns switch when in rtl mode:
theme/serenity/layout/frontpage.php
theme/serenity/layout/general.php

Change $bodyclasses[] = 'has_custom_menu' to 'has-custom-menu' , on all themes (for consistency with other css class names)
theme/serenity/layout/frontpage.php
theme/serenity/layout/general.php
theme/serenity/style/core.css