Indesign bug: RTL mark not working

Nope! He's not kidding you, and you don't actually need to install a Middle Eastern edition of InDesign with full controls for bidirectional typesetting that far exceed what you're going to find in any modern browser. But you do need to understand how that robust typesetting engine works, if you expect to salt your text with a few Unicode directional markers and have it respond as if it were text in a browser. (As you've already learned, it won't.) 

100% of the tools for handling RTL text are available in your install of InDesign; most of what is added in the ME editions are user interface tools to easily control bidirectional layout. For example, it's possible to turn an LTR paragraph into an RTL paragraph with a line of Javascript, if you don't have the ME edition installed. But if you need to handle any significant amount of bidirectional text formatting, it's much faster to just install the right toolset than it would be to go through your document and add Arabic letter marks (which I'd suggest in your shoes, instead of RTL marks). 

Assuming that you're actually trying to use the RTL mark correctly as you would in a browser (on a run of Arabic embedded in the midst of a fully LTR paragraph) then what you'd want to do instead is inform InDesign's typesetting engine that you want to assign the RTL property to a selection of text by using this line of Javascript:

app.selection[0].characterDirection = CharacterDirectionOptions.rightToLeftDirection

Assuming you're using Windows, you can navigate to your "Scripts Panel" folder located under \AppData\Roaming\Adobe\Indesign\yourVersion\yourLocale\Scripts and save it there as something like "applyRTL.js" then run it from the Scripts panel on any selected text.