Steps for extending FckEditor for Right-To-Left support (Short english version):
1. Open file: Providers\HtmlEditorProviders\Fck\FCKeditor\editor\fckeditor.html
after row window.document.dir = FCKLang.Dir ;
add FCKConfig.ContentLangDirection = window.document.dir;
2. Download from here FCKEditor Flow Direction Plugin
copy TextFlow folder from downloaded ZIP-archive to FckEditor plugIn derictory: Providers\HtmlEditorProviders\Fck\FCKeditor\editor\plugins\TextFlow
3. Open file Providers\HtmlEditorProviders\Fck\Custom\fckconfig.js and add FCKConfig.Plugins.Add('TextFlow', 'en'); into plugIns section
go to FCKConfig.ToolbarSets["DNNDefault"] section and add two entries: LayoutFlowRTL and LayoutFlowLTR
FCKConfig.ToolbarSets["DNNDefault"] = [
['Source','Preview','-','Templates'],
['Cut','Copy','Paste','PasteText','PasteWord','-','Print','SpellCheck'],
['Undo','Redo','-','Find','Replace','-','SelectAll','Removeformat'],
['Bold','Italic','Underline','StrikeThrough','-','Subscript','Superscript'],
['OrderedList','UnorderedList','-','Outdent','Indent','Blockquote'],
['JustifyLeft','JustifyCenter','JustifyRight','JustifyFull'],
['Link','Unlink','Anchor'],
['Image','Flash','Table','Rule','Smiley','SpecialChar','PageBreak'],
['Style','Fontformat'],['FontName','FontSize'],
['TextColor','BGColor'],
['FitWindow', 'ShowBlocks', '-', 'SyntaxHighLight2', '-', 'LayoutFlowRTL', '-', 'LayoutFlowLTR','-', 'About']
] ;
This is all