How to change text direction in the latest version?

Hmmm. I just changed the whole paragraph which includes both English and Persion to World-Ready Paragraph composer and seems to work for both languages. Fingers crossed it works throughout the book.

Yeah, PS and Illustrator both have some minimal complex-text handling tools. InDesign's handling of RTL text is rather more complicated & more robust, for a variety of reasons that probably don't interest you, but the upshot is that the tools for handling Arabic are exposed only in "Middle East/North Africa" versions of the app. The version I was directing you to download was the Middle Eastern toolset with the English language interface. So you wouldn't have an Arabic UI after reinstalling. The tools are all there in your en_US app, but they're not in the UI.

However, if you don't wan't to go through that reinstallation, you can just save this in your Scripts folder. All of those RTL-handling tools that are in the ME editions are in the plain vanilla English tools, but they're not in the UI, and are only accessible via script. I grabbed it from an article by Thomas Phinney about doing RTL work in CS4, so it's been kicking around for a while...

//DESCRIPTION: Toggles R2L and L2R paragraph direction to selected text
main ();
function main ()
	{
	try
		{
		if (app.selection[0].paragraphDirection == ParagraphDirectionOptions.rightToLeftDirection)
			app.selection[0].paragraphDirection = ParagraphDirectionOptions.leftToRightDirection
		else
			app.selection[0].paragraphDirection = ParagraphDirectionOptions.rightToLeftDirection
		}
	catch (_){}
	}

However, this will only work for you if you don't need to assign language, or deal with numeral style or numeral direction. If you have to do more than just flip the paragraph direction, you'd be best served by just downloading the ME version with the English interface. But, all these things are accessible via scripting, if you'd rather go in that direction.